Difference Between Essen and Fressen
Both words mean “to eat”, but the difference between essen and fressen is in who (or what) is doing the eating.
Essentially the verb ‘fressen’ is used when talking about animals eating, not ‘essen’, which applies to people: Menschen essen, Tiere fressen.
Fressen, as a synonym of eating when referenced to a person can be quite rude as it means “to gorge”, and should never be use it in a formal context except when talking about animals. If somebody eats too much, devours their food very quickly, and eats in a way that doesn’t look very nice, then fressen might be used, meaning he/she eats like an animal.
Essen (people) “Ich esse ein Steak”
Fressen (animals) “Mein Hund fraß sein Futter”
Fressen (people) “Er fraß sein Steak” (and probably won’t be invited to his friends’ house for dinner again).
Mind you, sometimes things aren’t so straightforward!