A guarantor is someone who agrees to pay your rent if you don't pay it, for example a parent or close relative. If you don't pay your landlord what you owe them, they can ask your guarantor to pay instead. 

Yes, you can appoint anyone (your parents, relatives, guardian, family friend etc,) to be your guarantor. They will need to co-sign the agreement and will be financially responsible if you are not able to pay the rent.