Follow the instructions to set up an Admin User Account (see related article).
To restrict an Admin User Account's access to specific Activities, you will need to set the Admin User Account to Role = Standard. The next step is to select the Activities the user is allowed to access.
Go to Settings > User Accounts
Next to the Name of the user, hover over the 'Action' column and click 'Manage Permissions'
Select the Activities the user may access and click 'Save' to update your changes
When the user signs in, they will be forced to select which Activity they want to work in before they have access to any data
