In order to invite someone to have access to certain parts of a website's administration, simply just navigate to your Profile Dashboard -> Admins
By clicking on Add An Admin you can invite a new team member to your website or project. They will receive an invite only to the specific website you are inviting them to.
An email will be sent to them with an invitation link to register and get into the website or project.
As the owner/admin, you always have the ability to change or remove someone's access from the same Admin tab.
