You can already before you sign up for an activity see if the activity is private or open for registration.
By a private activity is meant that the activity belongs to a team or a club, and that you first have to be a member of the team or the club, before you can sign up to the activity.
If the activity on the other hand is Open for registration, can you apply for participation without becoming a member of the team or the club.
This gives your club the freedom to choose, what activities there should be open to all, as well as which activities there only should be available for members of the club.
Click on the activity.
Scroll down and under Activity overview it shows, if the activity is open for registration or private.