In my opinion,
The best thing you can to is to start with downloading this selection of XM chiptunes:
ftp://ftp.untergrund.net/users/rez/packs/xm.zipFrom these tracks you can watch how effects and techniques are being used, and you can rip instruments by using the save/load buttons above the instruments list. Or even use the "zap" button to erase "song" while keeping samples/instruments.
You navigate through sounds primarily by selecting instruments in the instrument list (shift-arrowup/shift-arrowdown). Soon enough you should start creating your own sounds.
1. In "Smp. Ed." (ctrl-s), right click on the empty sample and select "new". A dialogue let you choose the size of your sample, and i suggest using a size of 64 bytes as default.
2. Select "Forward" in the middle bottom area of the screen. This sets a normal sample loop.
3. Now, to fill the empty sample with some kind of waveform, you will have two options:
A) Right click on the sample area and select one of the waveforms in "Generators"
or
B) Hold shift while using your left mouse button to draw in the sample area.
Once you have done any of this you will have a chip sound by using your keyboard.
4. Use "Ins. Ed." (ctrl-i) to chance parameters like panning and vibrato. Try this:
Tick "on". Then start moving the dots far up left in the matris using your mouse. You are now editing the volume envelope and your sound should change accordingly.
Let me know if there are any problems or if there is anything else i can help you with.