There is an optional studio sideloader modpack. I would recommend not downloading that immediately.
Then once the rest is installed you will have 3 parts of the game.
1. the HS2 game itself which is a sex simulation game where you select characters, more positions & options open up as you gain experience.
2. Character maker where you can create, adapt, etc characters for use in the game itself and Studio
3. NEO Studio - a free format environment where you create whatever you want to see and do. The possibilities are almost endless with the only bounaries being your imagination, time and machine spec. You can set up your own environment (scene) or adapt someone else's. It can have multiple characters. They can move, dance, bang, fight, whatever you define. It's vast. You don't need the optional studio modpack to run it and use it. That modpack contains items that can be used in Studio. I can't remember the details but maybe some cars or a bondage rack or a palace or a viking outfit. It is a lot of additional items (mods) that aren't used in the main game that have been developed in order to expand the horizons of what people want to see and do in Sudio.
I would suggest starting with the main install. Get used to the Game and Character Maker and start looking at Studio. Start simple with that by downloading a few scenes created by others and seeing what they do, even just swapping in your own characters. Then at some point you can decide whether you want to download the massive additional modpack.
Best of luck.