Site permissions are set when a user is first created but can be edited at any time
Go to the “Settings” tab, then “Users”
Find the users that you’d like to add or remove a site from, and click “Edit”.
You will see a field labelled “Assign to Sites”. Within this field, enter the name of the site, and click to select the site(s) you want the user to be able to access.
If you want a user to be assigned to all sites, click the “Assign to All Sites” checkbox.
Click "Save" to ensure these changes are applied
To remove a site from a user just click the x by the site name.
Admin users are automatically able to view all sites, but you are assign their Home Site by selecting it from the drop-down menu on the “Select Home Site” field.