Scan the poster, create an account, pick a plan, and show up in the roster as pending — the self-registration flow from an athlete's point of view.

Most gyms on Compteam have a poster on the wall with a QR code. Scan it with your phone's camera — it opens a registration page that's already linked to that specific gym, so you don't need to search for it or type anything in.
No poster handy? Ask your coach for the gym's registration link, or search for your gym from the registration page.
Enter your name, date of birth, and an email address (or sign up with Google or Facebook). This becomes your personal Compteam login — the same account works if you ever train at, or switch to, another gym on Compteam.
If you're a kid, a parent or guardian creates and manages the account on your behalf.
No password is generated or sent to you by the gym — you set your own, and only you (or your guardian) ever know it.
Choose the membership plan you're signing up for — your coach can tell you which one applies to you if you're not sure. If the plan has a monthly fee, you'll be asked for billing details (e.g. an IBAN for SEPA direct debit) so invoices can be collected automatically once your membership is active.
You can also add your address here if the gym needs it for membership paperwork.

A few gyms switch on an extra check: when you sign up yourself, your request is held for the coach to approve before you become an active member. If your gym uses this, you'll see a "waiting for approval" message right after you register, and the coach is notified automatically.
You don't need to do anything — once they approve you, you can sign in and start using the app. If a coach declines a request you can simply register again later. (This only applies to people who sign themselves up: if your gym added or invited you, you're activated straight away.)
Once you submit the form, you're done. Your profile appears in the gym's roster as pending — a coach or admin reviews it and activates your membership, usually within a day or two.
After activation you'll see your belt, training stats, and competition history build up over time in the app, and you can manage your billing details from your profile whenever needed.