If you have the “Manage Team Members” permission (typically given to the Admin and Manager roles), you can invite additional users by visiting the Account Settings page. Navigate to the “Team” tab and hit the "Invite" button in the upper right corner of the page.
You will have to provide the following information:
Email: The new user’s email address
Role: This decides what permissions the invited user gets. See the Roles page for more information about each of the roles. NOTE: you will only be allowed to assign roles which have the same or lesser permissions than you. If you don’t see the role you’d like to assign, ask your Admin to invite the user.
[Optional] Login Method: Whether you want the user to login via a password (default) or your (optional) Single-Sign On Provider.
The user will receive a confirmation email to create their account.
Note: Should the invitation link expire, simply invite the user again.
For instructions on becoming an admin, please see this article.