Then read this first:
http://www.cs.uiowa.edu/~jones/step/

It is the best presentation of the theory behind these motors you are ever likely to find. The information there is correct, free and available at all times.

If what you seek is not there, then it gives you enough knowledge to put forward your question with enough information about your problem that it can be intelligently answered by someone here in the forum.

Print it out, find your couch, lay back and get wiser.