Firstly, make sure that the user you are trying to add to your channel/ team has a registered account. If they have not registered they will need to.
From the Apester dashboard, click on the icon on the right hand side of the screen and select Settings from the drop down.
On the new pop-up window, select "CHANNELS" from the upper menu, and then click on "MEMBERS " on the upper right side.
Enter the user's email and click on the [+] button.