On the Home Page, click the Menu button in the upper left corner to open the sidebar.
In the sidebar, click [Business Settings].
In Business settings, click the [Users] tab. This will show you all the current users on your account.
Click [Invite User] in the upper right.
In the box, enter the emails of the people you wish to add as users to your account, one on each line.
Once these are filled out, click [Send Invites]. This will send an invitation email to the email address you entered, which will prompt them to complete sign up and login for a new account.
All invites you have sent will be visible on the Users page and you can see if they have accepted or not and when they expire.