Angel pretty much said a lot, you choose the topic and you research on it. With my EPQ its not related to the uni course I want to take (my EPQ is related to space but I want to do civil engineering) however you will learn certain skills from the project that will be needed during uni years so that's another favorable part for when unis see you doing it. I know that Manchester, Liverpool and Southampton (especially Southampton, they have some EPQ system for grades where they may give 2 offers one which will contain the EPQ grade) like it, it depends on the uni because some will view it differently.