You can create loops and patterns to send back and forth, and if you both have the same VSTs, you can leave everything in MIDI and work on the project more fluidly. Add effects, more sounds and whatever else you decide! Feel free to do whatever works for you :)

You will be matched with someone with the same DAW so that you should be able to just send the project back and forth. You can do this independantly or you can call live on discord with screen sharing to work on the project together and create something awesome! 

Decide how you are going to release the song whether it be on youtube, soundcloud, or you can submit your demo to Kiri Records to be considered for music streaming services. This may include one person being a feature, etc.