There are Harry Potter areas in each of the two parks. The biggest thing is that you need Park-to-Park tickets in order to ride on the Hogwarts Express (train that takes you between parks). There is a mini show that happens on the train, and it's different riding in each direction. More on reddit.com

"Our shortest building is taller than the tallest building in Diagon Alley..." That's pretty cool actually. That means it is going to feel really immersive with the sightlines being closed in by tall buildings. More on reddit.com

Orlando has 2 (soon to be 3) Harry Potter lands - Hogsmead/Hogwarts and Diagon Alley, with the Hogwarts Express that goes between. (Epic is going to be the Ministry of Magic) Hollywood only has Hogsmead/Hogwarts with no Hogwarts Express. More on reddit.com

There are 2 parks, Universal Studios and Islands of Adventure. The Wizarding World is split up between the 2 parks, diagon alley in the former, hogsmesde in the latter. They are connected by a Hogwarts Express attraction that will take you between the two. You essentially sit in a train car and there is a projection in the window that is different each way. Universal Studios and Islands is connected within walking distance on property by their version of Disney Springs called Citywalk (look at a map of Universal Orlando and you'll figure it out) You do need separate tickets for each park unless you pay for the park to park ticket which you will need to in order to experience the Hogwarts Express (and you should) If you want to start some research and better understanding how it works, use ThePughTwo, RixFlix, and VincentVisions YouTube (just three of many). Go through their old videos and watch anything that looks interesting, you'll figure all this out quickly. I would reccomend PughTwos older videos as being the most noob friendly, explains how tickets work, and everything else. More on reddit.com