Google API provides the users with a level of flexibility for their data analysis. This feature is great for filtering out data in report that you want to see, or, on the contrary, want to leave out.
Filters are useful for more advanced Google Analytics users, but if you are just starting, the formulas that are pre-set can be a great way to get going.
Clicking on any GA widget will bring the set-up menu of the widget and you will be able to specify the segments, apply filters or both.
A more detailed explanation in my video bellow: