From the Manage Users tab you can restrict your Trainers', Managers', Team Leads', and Reporters' view. (Administrators cannot be restricted.)
First you will need to ensure the user's role has been changed to a Trainer, Manager, Team Lead, or Reporter. Select their name and under the Information tab click edit.
Change Role to your desired permission levels for this user. Hit save.
You should now see a new tab called Permissions. This is where you will be able to restrict what group(s) of users they can see. To ensure their view is restricted to only the users you want them to see, please follow the steps here to set up Groups.
Click edit and under the Permissions section choose "The following groups" and select each Group you want them to be able to access.