Synth program?

I am looking for something that works sort of like a synthesizer keyboard. I have seen people use Macs for music recording and they add drum beats in behind it. You make them up though so it's not like a premade beat like what's in GarageBand. Anybody know? Thanks.

You can use GarageBand, just hook up a usb midi keyboard.

GarageBand has a built in software keyboard so you can use that. You can also use your keyboard for musical typing in GarageBand.

Can I assign certain keys to parts of a drum set? Like "G" and "H" will be my double pedal and I can just hit them back and forth and it will make a double pedal beat?