GET / HAVE SOMETHING DONE

We can use have or get in a passive structure.
Example:

I painted my room.
(This means that I painted the room myself)

I had my room painted. 
(This means that I didn't do it myself. I arranged for a decorator to do it for me).

This means that we use Get or have something done when we want to express that someone does, did or is going to do something for us: 

have / get + object + past participle

I'm going to have my hair cut

Dad had his car repaired last week.