FL Studio is one of many programs that fall under the category of DAW, or Digital Audio Workstation. Programs like Pro Tools, Sonar, Cubase, Logic Pro, Reason, Digital Performer, Ableton Live, etc, etc, are all referred to as 'DAW's.

In layman's terms, it is a program for creating/composing/recording/editing music. FL is mostly geared towards creating computer generated music. You won't find any links on this site about getting your hands on a copy of FL, as probably 90% or more of us have attained it illegally, but do a little googling and a lot of anti-virus scanning and you should be headed in the right direction (hint: torrents) You can, however, get a free demo from flstudio.com. I'm not sure what the limitations of the demo would be. Once you've got the program running, feel free to dive into this tutorial, and hopefully you'll be on your way.

And if you're wondering why this is relevant to bandamp, it's because a lot of the users posting songs here write them in FL.

Hope this helps some! Drop me a line at willydavidk@gmail.com for more info if you're still lost.

Peace,
-David