fressen
to eat
Food intake in animals.
Der Löwe frisst das Zebra.
The lion eats the zebra.

to eat / to devour
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to eat
Food intake in animals.
Der Löwe frisst das Zebra.
The lion eats the zebra.

'Fressen' (to eat / to devour) is a strong verb. Pay attention to the vowel change from 'e' to 'i' in the 2nd and 3rd person singular in the present tense: du frisst, er/sie/es frisst.
Der Hund frisst am liebsten Fleisch.
The dog likes eating meat best.
Using the verb 'fressen' (to eat / to devour) for humans is a common mistake, because it is very impolite and derogatory. It is the neutral word for animals, but for humans it implies greed or bad manners.
Meine Katze frisst nur eine bestimmte Sorte Futter.
My cat only eats a certain kind of food.
In a figurative sense, 'fressen' (to consume) describes when something uses up a lot of resources. Typical objects are 'Geld' (money), 'Zeit' (time), 'Energie' (energy), or 'Benzin' (gas).
Die ständigen Reparaturen am Haus fressen unser ganzes Geld.
The constant repairs to the house are consuming all our money.
In the meaning 'to work through material', 'fressen' (to eat through) is used reflexively with the preposition 'durch' (+ accusative). The construction is 'sich durch etwas fressen' (to eat through something).
Die Feuchtigkeit frisst sich langsam durch die Wand.
The moisture is slowly eating through the wall.
The idiom 'einen Narren an jemandem gefressen haben' (to have a soft spot for someone) is a fixed expression. It means that you like someone very much in an almost irrational way. The person you like is in the dative case.
Oma hat einen Narren an ihrem jüngsten Enkel gefressen.
Grandma has a soft spot for her youngest grandson.
to eat
'essen' and 'fressen' both describe taking in food. The important difference is usage. For people, you normally use 'essen'. For animals, you usually use 'fressen'. When used for people, 'fressen' sounds very colloquial and often derogatory, for example when someone eats greedily or without manners. Learners may confuse the words because both have to do with food. The safe rule is: for people, almost always 'essen'; for animals, usually 'fressen'.

Die Katze hat gestern den ganzen Napf leer gefressen.
Yesterday the cat ate the whole bowl empty.
Im Kurs essen wir in der Pause zusammen belegte Brote.
In the course, we eat sandwiches together during the break.