Universal Orlando has two separate parks: Islands of Adventure and Universal Studios. There is a lot in each of the parks to see. I like to get the 2 day, park to park ticket. This allows me to go between both parks all in the same day. Harry Potter World is a very popular part of the park, and you will need the park to park ticket to be able to ride the "Hogwarts Express Train" ride from Hogsmeade to Diagon Alley if you want. Each park has many things to see and do, so it might be a little too much to try to do all in 1 day in my opinion.