You can do so by entering their name in the search bar or by navigating to Settings (click on your login name in the top-right corner) > Firm Users and clicking on the name of the firm user.

On the bottom-left of the Firm User Details page, you will have two options: (1) Share All Firm Documents, (2) Share All Templates

Selecting these options will allow the firm user to access all Firm Documents and/or Templates in the system.

This feature is particularly useful when adding a new employee to the firm's MyCase account.