How Do You Go About Teaching Your Self To Use a Synth?

hi there me and my buddys are in a band and we play alot of alternative rock with abit of nine inch nails mixed in, and i have been working with the pa system and **** but they recently asked me if i could start to get my head around useing synths like sort of nine inch nails, marilyn manson and tool kind of stuff trippy complex and oh so wonderfull i have just began to download a whole bunch of VST stuff but i would still like abit more information guide lines and software, i have not yet got a keyboard and i am on a very tight budget :(