Upon first login, each user chooses a nickname.
To add a guardian, you can invite them to download the application (“send an invitation” button on the trusted people/guardian page (button at the top right of the home page). They will thus receive a download link and your nickname to connect with you.
If your guardian already uses the application, click on “add a trusted person”, enter their nickname and add them!
For security, you must mutually agree to be the other’s trusted person.