My answer must, of necessity, be a lengthy one. Just like all movies, the right cast had to be found. There's also screenwriting, the budget, and many other behind-the-scenes normal stuff. You can always research those steps yourself. I'm going to talk about the real movie magic. You probably know Hagrid. Well, in reality, actor Robbie Coltrane, who played Hagrid, isn't quite that tall. Special effects make him look that way. Many things, like hippogriffs and thestrals had to be added in via computer, as the filmmakers were unable to use real ones. The broomsticks were of steel, with bicycle seats attached. They were then hung every which way from cables. The riders had to be strapped in so they wouldn't fall off. All in all, a lot of computer animation hass to be used for such movies. I could go on and on about theeffects, but I think this'll give you a good idea.
