"Subtractive synthesis" is what you're looking at with the Virus. You start with a sound (an oscillator, or several), and then filter (similar to EQ) and shape and process it to get the sound you want.
At its most basic, synthesis has three elements: Oscillators, Filters, Amplifiers.
Oscillators are the sound generators. They generate waveforms that you can hear, and are controlled in pitch via the keyboard.
The Filters control the brightness or mellowness of the sound over time.
The Amplifier controls the changes of volume of the sound over time.
Here's a good overall explanation of subtractive synthesis and common synthesizer controls as a whole:
http://www.geocities.com/SunsetStrip...8/2ansynth.htm
As soon as you get the TI you'll just want to play with the presets as they're excellent and comprehensive. Probably the most tweaked knob on any synthesiser is the "cutoff" knob. It controls the filter, making it bright or mellow. The "resonance" intensifies the frequency of the filters' cutoff at any given time, which makes for nice filter sweeps or sometimes acid-type dance sounds.
After a while it's good to load up an initialised sound and start tweaking to see what affects what. You'll be able to hear what each of the waveforms of the oscillator waveforms sound like (Sine = very dull and bassy, Triangle is dull and quite flute-like, Square sounds like woodwind, like an oboe, but is also great for drum-n-bass type basses, Sawtooth is the brightest sounding waveform and is the staple of trance sounds.)
You'll be able to see how the Amplifier controls can be used to control how fast or slow the attack or release is of a sound (if it fades in gently or immediately, or if it fades out gently or abruptly, etc.)
Check out Howard Scarr's Virus Programming tutorial, too:
http://www.zorchmusic.com/hscarr/Vir...al_English.zip
May take you a year to pick up everything, but you should get the basics quickly if you just play around and use your ears.
The manual is of course helpful.