"gotta" means "must"

There is a clear suggestive meaning in the title; with "it" left dangling as probably meaning intercourse. This is from https://www.forbes.com/sites/davidalm/2017/11/15/the-radical-politics-of-spike-lees-shes-gotta-have-it-reboot-and-the-women-behind-it/#21ef66794b52 "The 'it' has changed, in terms of what she has to have," said one of the writers, Radha Blank, during the panel discussion at the IFC. "This young, black, insatiable woman – yes, she wants sexual freedom, but she wants so much more; she wants a voice."

gotta = got to = must

"Gotta" is an informal contraction of "got to" (She's Got to Have It), and the title suggests there is something that she wants that she must have. I've never seen the film so it might mean more than that, depending on what the film is about!