FL Groove?

I guess you could do something with that. But the software isn't gonna do the most important part for you.
I mean, you could use LMMS, FLStudio or Anvil Studio, it doesn't matter, you could write something awesome, or something absolutely horrible and out of tune depending on your grasp of music. That's true with everything really.

If you can't get FL Studio yet, and don't want to use free alternatives like LMMS, you might want to just work with MIDIs, or a real instrument at first.
One of the most useful and easy things to learn first is to transcribe a song by ear IMO. It trains your ears to recognize note pitches, chords, and even scales, and it makes it infinitely easier to deal with music in general.

You could also try out to read these guys' music theory online book, and their online tools : www.hooktheory.com/site
To learn how a song is structured and how it works.
They got some pretty neat, and very simplified stuff for the average non-musician person to understand ! Though, I forgot my password, and never got to read it after I bought it ^^; So I can't really tell if its absolutely worth the small investment..