I use
Fruity Loops Studio. The stock content that comes with it isn't great, but if you get digital libraries and VST plugins (Virtual studio technology), then it can be a very powerful program. The best thing about FL Studio is that it's user friendly compared to other programs like Reason and Sony Acid.
The thing is, most of those pro musicians use real instruments along with programs, or they have synthesizers in a big studio. There's plenty of digital libraries and VST plugins you can get, but the worth-while stuff costs money, ESPECIALLY libraries. Native Instruments is a good company to look in to when you decide to expand your library, just be prepared to spend cash. If you want to pursue music as your career then by all means save up for this stuff. If its truly what you want to do then you've got nothing to lose, right?
If you're curious, a VST plugin is something like this:
http://www.vemberaudio.se/images/surge_150.pngSo many knobs and slides. I've been working with FL studio and such for years and I still don't even know what half of them even do. I don't really have a strong music vocabulary, which is a huge weak point for me. All of my skills have been learned through experimenting with FL Studio and trying new plugins. It's really a pain that I don't know my keys and notes like a real musician would, but since I don't plan on making money off my music ever, I don't bother to really pursue it.
My computer is the only hardware I use. I don't have any MIDI devices or instruments lying around that I can use to make a song with. My collective digital library consists of the following, as far as I can remember:
Absynth 4 (VST)
FM8 (VST)
Synplant (VST)
Renegade (VST)
Predator (VST)
Albino 3 (VST)
z3ta+ (VST)
Blue (VST)
Discovery V2 (VST)
Vanguard (VST)
Toxic Biohazard (VST, Demo comes with FL Studio)
Symphobia (the most incredible orchestral library in the history of mankind...)
Stormdrum Kontakt Edition (great drum library)
Being a one-man musician is great though since creating a song comes down to the personal level. I find peace when I make music, so most of my music is mellow or light. I have a few dark ambiances and some hard acid songs, but I love electronica, psychedelic, and down tempo genres the most.
Anyway, that's enough out of me. I hope this gets you on the right path. FL Studio is a fantastic program to learn from and I highly recommend it to you. Don't bother with expanding FL Studio until you have a firm grasp of the interface and how shit works. There's no point in loading your PC with new content when you don't even know how to utilize it.