It's not compulsory to be a member of GEMA or any other collection society for the purpose of digital distribution. You don't need to send us a GEMA clearance either. The stores must pay GEMA fees from their share of the profit, i.e. this fee is not deducted from your earnings.
GEMA payments from the stores are made based on the individuals named as lyricist, composer, and others involved in creating the piece of music. You can add this information in the release process after uploading a song by clicking on "Edit" in the "Tracklist" section.
Your releases will not be automatically registered with GEMA or any other collection society. Please contact GEMA directly for any questions regarding registering your music.