Ambience tracks, trailer songs, credits music, etc. you create all of these. In my opinion, the soundtrack may be one of the most valuable roles here. While every role is important, music is powerful and should be taken really really really seriously.
(You can send your demos in MP3, WAV, MP4, etc. even a screen recording works. Just don’t send files in formats like .zip or other suspicious types; if you do, your application won’t be considered.)

If you choose this role, you're probably a really cool person