>>1486054first thing you need is a DAW (digital audio workstation), aka a music making software that is compatible with MIDI. Garageband is free if you're on mac and is bretty gud for beginners, otherwise there's Reaper, Cubase, Ableton, FL Studios, Mixcraft... download trial versions for each of these and see which one you like the most.
Don't bother with Audacity, its shit and won't do for anything serious.
Next download MIDI files of songs you like, there's a bunch of sites out there that have midis for pretty much every song in existence, its not hard to find. Import the midi in your daw and then you can start experimenting with changing the virtual instruments, adding layers, drum lines if there aren't any, mixing things with equalizers, compressions, adding reverbs, etc...
Finally buy some good audio monitors, either some speakers or some high quality headphones. Mixing on shitty laptop speakers or earbuds is a really bad idea.
I'll take a long time before you can pull out stuff as good sounding as Astrophysics, a big part of making music on computers it trying to make it sound good mix-wise, which takes a lot of experience, tutorial watching and trial & errors. Don't give up!
sorry I can't help you more, I only make metal music with my daw, can't help too much for synth remixes.
