There are several steps you need to do to register a Supercell ID:
1. Go to the ‘Settings’ of Merge Mansion
2. Tap on ‘Sign in with Supercell ID’
3. Select “Login” if you already have a Supercell ID or “Register Now” if it’s the first time
4. Enter a secure email address
5. Type the verification code which is sent to the email address (if you are unable to find the email with the verification code, check your spam folder and enter the last verification code)