To manage users and groups you must be an administrator.
From the LiveWhale interface, click the "Groups" link at the top righthand corner of the screen.
Find the user you wish to assign modules to.
Check the checkbox next to the user's name.
At the top of the page, select the module you wish to assign or remove from the dropdown menu.
Click the "Go" button.
You may also assign/remove modules from a user in bulk from the user edit screen:
From the groups manager, click the name of the user you wish to edit.
Select or de-select modules under the "Authorized modules" section according to the desired access.
Click "Save this user".