You go to one of the Mears desks (located at either end of the Baggage Claim floor), check in with them. They issue you a voucher and collect payment (unless you payed in advance) and then direct you to the Mears stop, where your shuttle or bus will meet you to take you to your hotel.
As for tipping, we always do, especially if we get great service; but we are a special case as we have a wheelchair-bound DS, so we get a vehicle all to ourselves, and door-to-door service (certainly deserving of a tip). In all likelihood you will be on a van or a big bus. If you get good service (like help with bags, etc.), please do tip, while if you end up doing everything yourself (like on a reguar bus), there is not really any call for it.
Their phone # is 407 423 5566
Good luck!