When you made your resort reservation, you needed to tell them that you would be using Magical Express and give them your flight information.
Then they would have sent you paperwork - one luggage tag per person and paperwork so you could board the Magical Express Bus.
If you didn't do that, you need to call Disney today and make your reservation. I doubt you would have time to receive your paperwork now but you can pick up your luggage yourself at MCO and then check in at the Magical Express check in desk. As long as you make your reservation, you'll be fine.
The phone number I have for Disney Magical Express is 866-599-0951. I have used it in 8 months but I think it is still good. Otherwise you can call their main reservation phone number too.
Have a great trip.