You've created a website and now you want to invite someone to have access to certain parts of the website's admin. You can do that by going to Dashboard -> Contributors.
By clicking on 'Add Contibutor' you can invite a new person to the website. They will receive an invite only to the website you invite them. An email will be sent with an invitation link to register and get to their website. As a website owner you can always remove someone from the contributor's list.