Hi, Sharon!
What fun to have a beach day! It is about 1 - 2 hour drive, depending on which coast you choose. Your best bet is to rent a car. You can rent one from Orlando International Airport and have it for your entire stay, or for just a short term rental, you can rent from the Car Care Center right on Disney property. I am going to have you click
HERE to Disney Mom Whitney's answer, she has all the details on locations and center times if you choose to rent on-property.
As far as beaches go, you can take about an hour drive to the east coast to Cocoa Beach or Daytona Beach. If you want to go west to the Gulf Coast, Clearwater Beach is your best bet. Plan on about 2 hours to Clearwater. While Clearwater is further, I love the Gulf Coast. But, if time is an issue, Cocoa Beach is your closest option.
Whichever beach you decide on, pack your sunscreen, beach towels, and sunglasses and have a great day at the beach! If you decide to stay with at Disney and skip the sun and sand, you can always visit Mickey's favorite beach:
Blizzard Beach! Just a quick bus ride from your resort - a great way to get a touch of the beach without leaving Disney property. Have fun!