A database filter enables you to extract information from database file(s) that you want to print on the report. The ability to use filters in database programs has always been one of the strongest features of database applications (dBase, Foxpro, Access, etc). While they can be a little confusing at first, if you understand some basic concepts of how to create a database filter you will find them to be extremely helpful in creating useful reports.
Filters do not change any information contained in database file(s); they don't copy information to another file either. A filter simply "hides" information that you don't want to see, which explains why they are called "Filters". No matter how many times you create or use a database filter, you are guaranteed that they will never harm your database information. Hopefully this will give you the confidence to try creating filters for various purposes.