Hey Bourban
A filter is like a super strong eq. But instead of turning only the bass or treble up or down, it removes everything higher or lower than the bass (or the treble).
So you can be listening to a song where you like the bass, but not the guitar, run a filter over it and remove the guitar so you only hear the bass. This is called a low pass filter.
If there's a song with a nice cymbal pattern, you can cut out all the crap that is beneath it so you hear only the hats and cymbals. This is called a hi pass filter.
Easy
Dahkter