The control slider is not an image… I disabled mouse selection of the shapes in the outliner so you would not accidentaly move them around. Start up an “outliner” window and follow head => big_control=> (etc) to reenable mouse selection (click the mouse arrows on the right side of the outliner window)
Object mode vs pose mode: they would have used pose mode because they were using armature bones which need pose mode to move, but anything which can be measured in terms of position can become the “driver” for other things.
The X and Y azis on the IPO window control the influence of the slider against the each blend shape. Select the head in the 3D view, then choose either “smile” or “frown” on the right of the IPO window, then hit the “HOME” key (with mouse over the IPO window) to zoom in for a good look. The “basis” shape is always 0, which goes up to 1 when a blend shape is on. So, if a blend shape is half way, then it would be 0.5. The Y axis (left side) is this blend shape and the X axis across the bottom reflects, in my example, the Z axis of the slider bar (how far up and down it has been moved.
So… in the example I made you, the slider bar position is “rested” at 0, but can move as high as +4 or as far down as -4. If you look at the “smile” IPO line, it ranges from Z=0 with blendshape=0/off through to z=4 with blendshape=1/on. You see? Move the slide controller from 0 up to 4 and the “smile” blendshape changes its influence from 0 to 1. On the “frown” curve, the Z position of the slider goes down to -4.
To be honest, it’s fairly tricky at times and I had a couple of guesses as to which way was X and which was Y as I was making you this example. In Maya the “expression editor” is much easier. You can just say “blendshape = slider.posZ / 4 (but only when slider.posZ>0)”. This is also true in Blender (python expressions) but Maya’s is simpler to use and can have much better expressions.
Have separate sliders: one for smile/frown, another for wide / narrow mouth, another one for open/close jaw (or just rig the jaw to a rotating jawbone). This way, you can mix the sliders… have it smiling with narrow mouth as well as frowning with narrow mouth.
The slider indirection is local by the way, meaning you can make the head do cartwheels and it won’t put the slider off. Use the middlemouse wheel to rotate the view for better angles to look at the head an slider.
Don’t worry about asking questions. You’re attempting something fairly complex here. Hopefully I’m not babbling (a few too many late nights).