No answers yet, so I'll put in my 2 cents.
A more aggressive edge (3+ degrees) bevel will cut into ice better, improving turns, but making the skis more itchy (squirrel-y?). A less aggressive edge (0-1 degree) won't bite as easily, but wears down slower and is more comfortable to ride for beginners.
The base bevel and side bevel can both be changed, but typically you only sharpen from the sides once everything is set.
There are two ways to apply this angle change. One is by eye, using a file. This method isn't very reliable for a consistent angle, but unless you're skiing really hard you probably will do just fine. You can wrap a little tape around your file to tilt it upwards a hair as a simple guide.
The next method is using a fixed bevel tool or a multi-angle tool. Ski shops use the fixed ones because they are the most reliable and consistent, but they are also more expensive (for reference, see this bevel tool, which costs $20, and you only have one bevel option). These tools typically accept either a diamond stone or regular file.
Don't forget to de-tune the first few inches of your skis when you're done! To "de-tune," you run a file at a perfect tangent to the edge (you are making it slightly dull, taming that beautiful sharp edge you just made) for the first few inches of the ski's edge (beginning around the point where it will actually contact the snow). You do this because a very sharp tip or tail edge can cause your skis to be difficult to control. Imagine catching a sharp edge that far from the controlling force of your foot - not fun.
There are several good websites that provide more detail and specifics:
Racewax.com, Telemarktips.com, and Tognar Toolworks all have detailed writeups. I doubt I could write something better here.