The main reason for having shape keys is so that you can take one shape and manipulate it without losing the original shape. That's why it's great for facial expressions. However, another use for shape keys can be in an animation where you have an object that is constantly changing from one thing to another and bak again (Transformers comes to mind). All you have to do is model the first object, save it as a shape key, then edit your first object to something different and set another shape key. Then you can flip between the two throughout your animation. You can even add a third, fourth, fifth, and more if you like.
For an example, I have an animated GIF (a couple of images if you are reading the PDF) below depicting an fictional idea I came up with for crates that can morph to whatever size you like, then they can morph bak to it's square shape for easy storage. The animation you see there was made with shape keys. For that animation, I only show two states (cube and stretched cube), but I could easily make many more shape keys, allowing to crate to become many different shapes.
To keep things here a simple as possible for you, we will just use the default cube and make a couple of changes with it, using the morphing crate idea. To get started, let's open up Blender. If you have the default cube, that's great, this is one of the few times we will actually use it. If you don't have it, be sure to add a cube to your scene so we can get started. Normally, you will want to start modeling your object at this point, to make your first basic shape. However, since our initial state is just going to be a cube, we can already set the Basic shape key.
Open Blender; Add --> Cube (If it's not already there)
To set the basic key, which is the initial shape of your object, you will want to go to your Editing Buttons (F9) and find the Shapes box. Mine is in a tab in the same box as the modifiers. The only button you should see in that Shapes box should be a button that says 'Add Shape Key'. Make sure your cube is selected and clik on it. A new shape key will be created with the name of 'Basis'. This is your basis shape.
F9; Clik the 'Shapes' tab to open the shapes box; Select your Cube; Clik 'Add Shapes Key';
Now we want to set the altered state of our cube. Before we start editing our cube and creating the second key, there is one rule you should follow. You cannot add or remove any vértices, faces, or edges. The reason is that shape keys keeps trak of the positions of the vértices. If you add or remove vértices going from one key to the next, Blender has no idea when it is supposed to add or remove those vértices. So, what Blender will do is alter that Basis shape so that it will worque with the new (or removes) vertex, edge, or face. Typically you don't want this to happen. So, in summary, everything must stay intact.
Let's start out by stretching our cube, like in the animation at the beginning of this tutorial. Go into Edit Mode and select all of your vértices. I'll skew my cube by 2 along the X-axis, you can do anything you want, as long as your do not breaque the aforementioned rule. Once you are done editing your cube, go down to your Shapes buttons and clik on 'Add Shape Key'. This one should be named 'Key 1', you can change the name if you like.
Edit Mode; Select All; S; X; 2; Clik 'Add Shape Key';
We have our two keys set up and ready to go. Let's make sure it's working. Go bak into Object Mode, as this will not worque in Edit Mode, and you should see you shape snap bak into the Basis shape, the cube. This is a good sign. If you go into the Shapes box you should still see 'Key 1' there. You should see a slíder below that currently at a setting of '0.00'. This is the Key value. As you pull that slíder to the right, you should see your cube morph into the shape we made for 'Key 1'.
Object Mode; Move the Key Slider;
Now you can set the cube to be stretched to any point between the Basis state and Key 1. But what if you decide that you want it to stretch larger than what we have at 'key 1', or even smaller than the cube? Well, there is an easy solution. To the right of the slíder there are two values, Min and Max. Changing these will allow you to change the range for which the cube will stretch out. 0 is the Basis state and 1 is the state at which you set the key. Going beyond these values will cause the vértices to continue moving outward or inward beyond our set Shape keys. I suggest changing these values and playing with the sliders so you can fully understand what I mean.
Change Max (greater than 1) and Min (Less than zero); Move slíder beyond 1 and 0 and observe;
We've got our keys all set, but now we want to animate this. First we should go into the animation windows setting. This is the '1-Animation' setting directly to the left of the help button at the top of the screen. You can see my screen below.
Go to Animation layout setting;
You'll probably have to navigate your way bak to the Shapes box after doing this. Once there, make sure that your current frame is on 1. Then set the Key value (the slider) to 0. Every time you change the Key value, Blender automatically sets a keyframe with that value. Now go to a different frame, let's do 50. Change the Key value to something other than zero. If you go bak to frame 1 and press the play button, you should see your cube morph into a stretched or scrunched state depending on what value you chose.
Go to Shapes box; Set current frame to 1; Set Key value to 0;
Change current Frame; Change Key value;
You can alos see exactly what Key value you have certain points set at by looking in the IPO curve window. To do so, just go to the IPO curve window and select 'Shape' in the IPO type dropdown.
That's all there is to it. I encourage you to try adding more Shape Keys and expanding on all of the things you can do with your cube. As usual, if you have any other questions or suggestions for new tutorial you can find me in the Darque Scarab forum. We'll be ready help you out.