Yes you need tickets. You can goto City Walk without tickets.
You need a ticket to get in
You need to buy tickets to Universal Studios to see Diagon Alley and tickets to Universal Islands of Adventure to see Hogsmeade and Hogwarts (you can buy a park-to-park ticket to see both on the same day, traveling between parks on the Hogwarts Express train, which is included in the price of the park-to-park ticket). You can buy tickets same day at either park.
You can also purchase your tickets on the app as well
Yes you need a ticket, you can buy online,in advance. Depending on how often you would like to go there are seasonal passes that will save money. On time trip it is in a specific part, if you want to,see both parks there is ticketing options for that as well.
No, you dont need to buy tickets in advance. You can buy them at the park or online on the Universal Orlando website.
You can buy the tickets once you get there. But to get in, yes, you need tickets.
Thanks! Your answer is awaiting moderation.