Filters are saved searches that you can use to organize and sort your list of people in your database.  

In the People tab of the control panel you can view an overall list of everyone in your database. There are four different drop downs that allow you to sort this list in various ways. The third drop down from the left is reserved for filters.

To create a new filter go to the advanced search tab. Here you can choose from a variety of fields including basic, location, donation, and contact information. You can choose to pull your list based on any of these or any combination of these. Below the search fields click the Search button to see your list change based on the fields you are entering data into. When you are ready you can click Save as Filter. Once you've saved the filter, you will always be able to go back to this particular advanced search from the filters drop down in the People tab.