When do i use y or en in french?

Y - Replaces a phrase beginning with a or a preposition of place

Je vais au parc. I'm going to the parc J'y vais - I'm going there.

En - Some, any, of it - Replaces a phrase that begins with a form of de(de, de la, du, des)

Nous achetons des bananas - We're buying some bananas.

Nous en achetons - We're buying some.

But there is also a case when y can replace a thing.

If you are saying something with a verb that uses à after it,

for example the verb "penser à" and want to use a pronoun

you would have to use y

EXAMPLE:::: Je pense à ma voiture.

I think/ am thinking of my car.

You would change it to: J'y pense. (I am thinking of it)

BUT IN THIS CASE YOU ONLYYYYYYYYYYYYYYYYYYYYreplace

nouns that ARE NOT people!!!!! :)

hope that helps!