They enjoyed themselves at the party.

A form of the pronoun used to refer back to the subject of the sentence, indicating that the action is performed by the subject on itself.
The children played by themselves in the yard.
She taught herself how to play the guitar.
He looked at himself in the mirror.
enjoy themselves
find themselves
teach themselves
oneself
yourself
himself
They made the cake themselves.

Used to refer back to the subject of the sentence when it is plural or when the subject is "you" in a formal context.
The children dressed themselves.
The team prepared themselves for the game.
You should remind yourselves of the rules.
enjoy themselves
find themselves
help themselves
themselves
each other
one another