Here are some examples:
* Dejar la casa: To leave the house.
* Dejar la puerta abierta: To leave the door open.
* Dejar que el perro entre: To let the dog in.
* Dejar de fumar: To quit smoking.
"Dejar" can also be used in a more figurative sense:
* Dejar una buena impresión: To make a good impression.
* Dejar de lado las diferencias: To put aside differences.
The exact meaning of "dejar" will depend on the context in which it is used.