You can make Dubstep with any music making program. I use Fl Studio 11, but there are many others available as well like Ableton Live, Reason and Cubase for example. You should start by watching some tutorials and downloading the demos of the programs. When you find the one you like the most, you can either buy it if you want to support them, or torrent it if you don't have enough money. I reccommend watching SeamlessR's tutorials on YouTube. He's pretty good and he also uses Fl Studio!