Index (this will be updated as the series unfolds)
Part 1a: Importing Files and File Types
Part 1b: Camera Raw
Part 2: Colour:
Part 3a: The Workspace
Part 3b: Example Layers Workflow
Part 3c: Adjustment Layers
Part 4: Grouping, Masks & History
Part 5: Selection & Paths (Pen Tool)
Marquee
Magic Wand
Quick Selection
Lasso
General rules
Paths / Pathing / Pen Tool
Anchor Points
Convert Points
Making selection
Feathering
Part 5b: Healing Brush, Patch or Clone Stamp Tool?
Selection and paths:
The Marquee tool offers shape-specific, simple selection processes, but there's an abundance of other tools for specific and at times complex selection. After all, what's the point in having layers if you can't put what you want into them?
Magic Wand
The Magic Wand is best summed up as 'partially useful'. It's useful because if you click on a specific part of an image, it can highlight areas elsewhere on that image that have similar colours or tonal values. How tolerant this selection process is can be controlled by adjusting the ingeniously named 'tolerance' - the higher the tolerance the more the tool will select.

Caption: Tolerance can be adjusted here
Magic Wand will not make a 'general' selection - those small spots in the middle of the selection are not part of the selection, so copying/cutting away will leave those fragments behind. To those people that go straight for the “magic” wand, think twice; there are better selection processes. These processes may be more time consuming, but provide significantly better, more professional results.
Quick Selection (CS3 only)
Owners of the latest version of Photoshop (CS3) get to see just how limited the Magic Wand tool really is, because they can compare it with the new Quick Selection option. Instead of a single click, Quick Selection allows you to click and drag the tool around, which generates a fuller selection based upon your mouse action.
Quick Selection is also a smart tool, as it has the ability to find edges and 'think' for itself… of course, this does bring some rather assumptive selection, but can work wonders with defined edges within an image.

Caption: Good for three seconds work, but it would have been nice to keep the hair selected too!
Lasso
This comes in three flavours - Lasso, Polygon Lasso or Magnetic Lasso.
The standard tool is a free-drawing device, where you click and drag the mouse to generate a selection. Word of advice however - drawing decent shapes by hand with a mouse is really, very difficult. It's ideal if you have a nice graphics tablet and you are a dab hand at the whole drawing malarkey, otherwise you may find it tricky to use well.
The Polygonal Lasso functions with the same idea, but each click of the mouse will draw a straight line from the previous point. This means your final selection will be, surprise surprise, a polygon. This tool is ideal for selecting down some straight edges, or making some neat adjustments to edges, but soon stumbles on the more crinkly bits of your image.
Magnetic Lasso is similar to the Quick Selection tool, but probably better. As you guide the mouse around the screen, the selection becomes based on your movements, affixing to nearby edges in the process.

Caption: Each square is an auto-generated anchor point that occurs during selection.
General selection rules
Not happy with the selection made? It's possible to add and/or subtract areas from the selection utilising any selection tools as outlined above.
Too add to selection, simply hold Shift and a small + symbol will appear by the icon.
Too subtract from a selection, simply hold Alt and a small - symbol will appear by the icon. Use as before and the selection will add to the existing selection.
To invert a selection, the quickest way is to press (Ctrl+Shift+I). It may not be apparent that the selection has shifted, but there should be apparent visual shifting of the selection by a couple of pixels.
To deselect, the quickest way is to press (Alt+D). This will become oddly useful and save you from taking a hammer to the computer at times.
Certain Photoshop functions can be interrupted by selections, so if you are unaware that you have an area selected, it may take you a while to figure out why things aren't working as you planned.
Selections can also be used to control where an action can be applied - making a selection and then brushing into it, for example, will not exceed the edges of the selection:

Caption: A rough example to demonstrate the uses of selections containing actions.
Pen tool / 'Pathing':
The pen tool (P) is the way to make selections, a process that pros may term as 'pathing'. It takes practice and can be frustrating to learn, but once you have a good understanding of the control at your disposal, it is the perfect way to accurately make and save selections.
Anchor points
Select the pen tool and click on your image where the initial part of selection is to start - this will generate your first anchor point.
It is now possible to generate more anchor points - which is where the course of the selection path will follow. Should you simply click each anchor point down then the tool essentially functions as per the Polygon Lasso -useful in some cases, but not the overall goal of pathing.
Convert Points
When applying anchor points, click and hold the mouse button down whilst dragging (slowly) to pull the Convert Points from the anchor. These points control the direction that the path will continue upon, adjust the curve of the path in relation to the previous anchor, and also the severity of that curve dependant upon distance dragged from anchor.
It's confusing at first and difficult to describe easily; it's something that's best to learn through practice. Here's some examples:

A: A near-complete path. Each anchor point can be seen and the relevant curvature of the path that follows due to such positioning.

B: By adjusting the convert points of two anchors (1 and 2) it is possible to see the adjustments made to the path's curve.
Adjusting Convert Points
Image A is a near complete path, Image B is the same path but with some adjustments on two anchors to show how the convert points adjust the curve of a path.
Point #1 has seen the convert point moved from its original angle - let's say 'four o'clock' - back upon itself - eleven o'clock - making the path that follows based on this orientation. Seeing this difference visually allows for you to begin to gauge and understand the placement of anchor points - they cannot be placed haphazardly, as their placement is integral to the accuracy of the final path.
Point #2 has seen the convert point moved from the two o'clock position to a horizontal three o'clock position. It has also been extended - this added length has incremented the severity of the path's curve.
When placing an anchor it is possible to manipulate the convert points by pressing and holding Alt. The cursor will change and the points can be moved, extended or shrunk as desired. Alternatively the Pen Tool in the Toolbar has a series of options that includes Convert Point Tool.
Adding/Removing anchor points
It is also possible to add new anchors to a path or remove undesired ones:

Caption: Example added anchor point. By default the anchor will have standard convert points that can be manipulated following placement.

Caption: Example removed anchor point, potentially can cause havoc as the curve will now be based for the position of the previous anchor and convert points. Note the severe backing of the curve towards the right corner of the lips.
One of the best things about making a path over a selection is that the always remains available. In the Layers window there is a Path tab - clicking this will show your work path (auto-generated when using pen tool), and offer the possibility of making new path layers.
Making new path layers allows for new paths to be drawn on separate layers that can then be individually summoned at a later time.

Making selection (path selections)
The purpose of a path is ultimately to generate a selection. However a closed path doesn't function as a selection until it is told to be - this can be achieved in two ways. Either right clicking the path itself (on the image) and select Make Selection or right click the path layer in the Path window and select the same option.
Note - the Pen tool needs to be selected in order to re-engage with a path.

Feathering (path selections)
An option will come up asking the Feather Radius of the selection.

This is important as it represents the portion of the selection edge's blend (to transparent. Selecting '0' will keep a fine edge, whilst opting for a few pixels will add an extra blend to the selection's edge. Selecting a larger number of pixels will blow the original selection significantly.

The vertical lines on the image above demonstrate the different feather radiuses and how they subtly blend to transparent to varying degrees.
Continue to Part 5b: Healing Brush, Patch or Clone Stamp Tool?