Details? Well, I only played once and it's been a few days, but I'll try.
Hinata is in the spare room at your house, you can only access it at night. In order for her to appear, your namigan has to be a high enough level, and I think you need to do the two S-rank missions.
Once she appears, you can only talk to her in the spare room at night and she doesn't do anything because she's depressed about her missing family and Himawari being a traitor and stuff like that.
Once you've talked to her at night a time or two, I think, she'll show up at the school during the day if you talk to Sarada, then you talk to her at night again, maybe, and move on to talking to Himawari. When you train with Himawari in the forest, instead of using the Namigan or actually training, you can talk to her and one of the talk options is asking about her mother, you might need to do this a time or two, but that will get her to meet with Hinata. I don't remember the specifics of the meeting, but the game made it pretty clear how that meeting would occur, so just read the end of the dialogue and you should be fine.
Once that's done, you can interact with Hinata at night. Spying on her gets you nothing but a look at her tits. Waiting for her provides the option to talk, train, or use the Namigan. Play with the options a bit and something happens. Don't really remember the details. However, pretty early on you'll need to go to Sarada's house at night and look around, this will take you to the past to train with younger Hinata, a la what you do with Himawari.
From there, some combination of training with Hinata in her three forms will progress her paths along through the story.