You may create/assign a category to a case during case creation (or category can also be added via case edit).  A case category is a self defined name, such as "Criminal Law", "Family Law", "Estate Planning", etc. to help manage large number of cases efficiently.  Having cases properly categorized will limit the listing of cases when the "Cases (Projects)" tab is clicked.  

To assign category to a new case:  on Add Case dialog box, next to Case Category dropdown, click on Add Type link.  Enter a new name and click on Save.  Then select appropriate category in the dropdown box.

To assign category to an old case:  Click on "Cases (Projects)" tab.  Select the case.  On the right side, click on "Edit Case" tab.  Select an appropriate category in the Case Category dropdown.  Click on Add/Edit Type link to add or edit a category.