Making samples is a complicated topic for sure. I don't know where to get started, but I think you should get a good sample editor (I use CoolEdit96, it's old but it's still as good as most other sample editors). There are a lot out there, although many are expensive. I believe Jojo has a good sample editor he could recommend.
What you should learn first is the characteristics of the sine, saw, square and triangle wave and the white, brown and pink noise. Then you should experiment with things like amplify, distortion, stretch, frequence filters, resonance, reverb and decay. It takes time and lots of work, but eventually you'll be an audio technican of elite caliber.
If you'd like, I could attempt to write a tutorial in sample making. The stickies in the Tracker forum contains older tutorials that I have written, maybe this one could be of use...
http://www.modarchive.com/db/boards2/viewtopic.php?t=139Although it's about fixing your samples IN the tracker and not about _making_ them. :|