How to get started with tracking music
First, pick a tracker of your choice, depending on your needs, this can be the very complete Renoise tracker, or alternatively Buzz.
Or you can choose to work with a vintage tracker, or a remake of a vintage tracker.
Install this application, using an emulator where needed.
The real stuff is always preferred, but even then, an emulator is a handy tool.
Second, search for a music module in the format of your tracker, and explore the program you have chosen.
Look for the help section, forums, attached textfiles, online manual,... Try to get familiar with the basics.
Third, you'll notice almost all trackers work with PCM sound samples.
Music starts with the sound, so you should create some sounds of yourself and sample them.
Owning a synthesizer is an immediate rich source for creating rich sounds.
Sounds can also be created by a program like PatchWork, which creates short waveforms with your own defined harmonics & symmetry.
Renoise, Buzz and some other programs support using VST synthesizers as sound source next to, or instead of samples.
Cybertracker on the Commodore 64 doesn't use samples or virtual machines as sound source, but the SID music synthesizer chip in the computer.
Fourth, you need to load the samples and/or virtual machines in your tracker.
Most trackers allow you to create an 'instrument' from your samples: applying envelopes, vibrato, tremolo, ... to your sample.
Virtual machines feature a series of parameters which can be manipulated.
On Cybertracker, instruments are where you define your whole sounds by manipulating settings for the SID chip.
Apart from Virtual sound generators, or VST synthesizers, trackers supporting virtual machines also allow you using effects on your tracks, both on samples and virtual machines.
Play with these things.
Fifth, when you have some sounds together (be sure you have saved a few times by now!), you can start composing in the pattern editor.
This is the most important part. Here you are composing and producing at the same time.
Trackers have an effect collumn, be sure to check out the different commands while composing your first shit.
They allow you to manipulate your sounds & virtual instruments creating richer variations in your tracks.
SixSixSixth, find your own ways and implementation of music trackers.
The treasury of different techniques possible is endless, while gaining experience, one can find tricks that might never have been done before...
Trackers can be used to produce an entire song, be used as beatbbox or drum-computer, to cut-up existing music, use it as sound generator to create loops or sounds to use again in a tracker or other musical applications, ...
Although not the easiest way to compose music at start, once understanding the tracker interfaces well, they are very powerfull and detailed tools for music and sound creation.