If you're flying from Orlando International and taking advantage of the Magic Express, you'll get a tag on your hotel room door on the day before you're due to depart. If you're flying from Sanford, you would have been given pickup information when you got dropped off. Make sure you're outside the main hotel lobby at least 20 minutes before your pickup time either way.
If you're flying from Orlando International, get off the bus and head up the stairs. You'll see all the check-in desks. Find yours, and check your luggage. You'll then go through the section with all the shops, you'll want to spend some time in here, especially if you didn't spend any time at the malls. You'll then go through security, head back on the monorail over to the waiting area. Keep in mind after you go through security and on the monorail, the only shops the other side is a duty free shop, a snack store, and a couple places to eat. So check out the shops in the airport before hitting security.
Sanford is a tiny airport, so it'll be a struggle to get lost. As soon as you enter the door you'll see the check-in desks, then you head left up the stairs through security. And that's it! You'll be in the room with the duty free and shops, you wait in here until your gate is ready.
You'll then board your flight and head home. When you land, have your passports through to go through UK border control.