If they've not registered with ClubSpark before they will have to create an account with an email and password or sign in through their LTA credentials.
NOTE: Junior members under 13 cannot have their own login / account so a parent will need to create the account.
Once signed in, they will have to accept your venues terms and conditions (T&C's) and opt in or out of any consents that have been created.
Clicking continue will take them to their profile page. Here they have the opportunity to update their contact details that the club holds.
They will now be a registered member.