The verb dejar (conjugation) is regular. It means to leave or to let. The conjugation is shown in the table below.

No, los dejé en casa con mi bufanda.
No, I left them home with my scarf.

¿A quién le dejaste tu maleta?
With whom did you leave your suitcase?

¿Por qué dejó la maleta aquí?
Why did he leave the suitcase here?

¿Por qué dejó su empleo anterior?
Why did you leave your last job?

Ellos dejaron la puerta abierta.
They left the door open.

dejar is also used with the preposition de which means to stop doing something.

Dice que no puede dejar de verlo.
He says he can't stop looking at it.

Debes dejar de fumar.
You ought to stop smoking.