Essentially, you are tweaking the data so you see what you want to see inside your reporting views. They take out the stuff you don’t want, or include the bits that you do.

Common examples for filters in Google Analytics are removing staff, if you have a static IP address and lots of staff all going to your website every day, they’ll show up as users and sessions, and that’s going to mess up your data.
Another example is to create filters to zoom in on users and sessions from a particular country for instance only looking at traffic from the USA, or the UK.
As you can imagine, filters are really powerful, they can clean up your data so you see only what you want to see, rather than scratching your head in confusion at misaligning data.
Go get our filter explainer template to see how they work in GA.