Register your interest in any gig by clicking the grey jack on any gig card in the bottom right corner of the event listing. Once it's purple, you've successfully shown interest. You can show interest either via the gig feed itself within each gig listing, or click into the expanded gig card and show your interest there.
Check out the images below to show how this works in Muso:
Viewing an event listing:
2. Event listing display after showing interest in gig: