My first post! Yay!
I'm not exactly good at any of this stuff, but I can say with a little bit of confidence that first you need the basic tools to get started. Then, using these tools, try to duplicate some of these songs you hear... you have to learn how to use your setup first. Just keep doing this with different songs until eventually using the setup becomes second nature and you don't have to think about it. That's when the bottleneck between what is in your head and what comes out becomes negligible.
From there you can do anything really... if you want to remix a song then you can do what these kind people said and load up a midi, or play it by ear. Personally I like to listen to the song myself and recreate it instead of loading up an already created version of it... they aren't always so accurate in my experience.
