You can register a new parent/guardian 1) during registration for new child, or 2) with the "register new guardian" option found on the database page. At minimum you must provide their name & phone number.

A parent or guardian can also register themselves by setting up a guardian account on the mobile app (they'll also need an email address in addition to name and phone number).  See "Mobile App: Creating Guardian Account (Parents)." Note: If you've already registered them in your database, the contact information must match (name, phone, email, etc.) in order for the account to sync with your database. If a parent uses a different number, mistype an email address, etc., while creating their account, the system will create a whole new account for them. This can result in what appears to be duplicate accounts. Simply go through and figure out which one has the correct information and delete the other one. 

For more information regarding adding a volunteer, see "How to Add a Volunteer."