Seeing as you are probably too young to rent a car (and assuming you are not coming with your parents) you may want to take an MTA (Maryland Transit Authority) bus. It takes about an hour from Annapolis to downtown DC.
Take the bus to 18 & K NW in DC and then you can grab the DC Metro at Farragut WEST and take it down to The Mall, or walk a few blocks south and you'll be at the White House.