Hi Amanda!
Congrats on your resort stay! You're going to find it hard to go back to off-site property once you've stayed on.. :-)
Yes, generally the resort that you're staying in will go ahead and grant you access to all their amenities, even if it's before the check-in time. This includes the pools, arcade, dining, stores, etc.
They also will give you any vouchers you're entitled to, and your Keys to the World Card, if, say, you want to make a trip to the Parks first before checking in. Makes life so much simpler doesn't it?
Have fun, relax, and enjoy the resort!