Normally, we use “salir de” when we want to say that we “exit from one place”. For example: salir de casa, salir de la universidad. It can mean other things too: salir de noche (go out in the night), salir de día, etc.
We use always de verb “salir” with something else: salir con amigos, salir mañana, salir a correr. As you can see, this verb can be used with different prepositions and you should learn all the structures by heart.