An employee does not sign up on this page. The company owner creates the account.
The owner signs in.
In the top menu, open Settings and choose Staff.
Press Add employee.
Enter Name and Email. The email is the login. Phone can be left empty. Set Interface language, Background color, and Text color. These colors mark the employee on the calendar.
Tick Send login credentials to email the password to the employee. Leave it unticked to pass the password on yourself.
Press Save. The service generates a password and shows it at the top of the page. The employee then signs in here with that email and password.