Within Teamwork Spaces, you can add users to your site individually via the People section.
Note: Only administrators can add people to your site.
In the top right of the People area, click the green Invite people button.
The Invite people modal allows you to add the email addresses of the users you want to invite.
Once added, an email invitation will be sent to the new user to complete their account setup by setting a name and password.
Note: New users will automatically be added to the owner company and inherit the owner company permission level.
For more information, see: Working with the People area