-> Have/get something done (Causative) is used to mean:
. cause something to be done by someone else
e.g. I had/got my hair cut yesterday. (The hairdresser did it.)
. cause something to happen yourself
e.g. I´ll have/get this mess cleared up in no time.
. experience something (usually undesirable)
e.g. Clara had/got her credit cards stolen the other day.
Get is used rather than have:
. to show a feeling of obligation or urgency
e.g. I must get my car insurance renewed - it ran out last week!
. to show that something was difficult to do/achieve
e.g. We finally got the decorating finished just before we moved in.
. to indicate a planned action to achieve something
e.g. He got himself elected President of the club.
. in imperatives
e.g. Get this room cleaned up at once!