Y

y replaces prepositions: à, au, aux, à la

y replaces the names of locations

it means "there"

y replaces a prepositional phrase that is introduced by a preposition of place or direction, other than de

y precedes the verb

y is used to replace the object of a verb followed by à, if that object refers to a thing

when noun following à is a person, noun is the indirect object of a verb, lui and leur are used

if y occurs with another object pronoun in the same sentence, it follows the other pronoun

In sentences with en, y precedes en

Example:
J'y assisté