Getting Started
High School Simulator 2019 Guide
As soon as the game starts (after picking a preferred gender in the main screen), you'll be tossed in front of school campus. There won't be any guides, tutorials or any objectives at all. Not even hints on how to play the game - aside from the on screen game buttons that you see and your character in the middle of the screen. Knowing that the game is powered by a unity engine, probably is the only hint that tells you an in-game directional jog should at least be present (given its three dimensional nature).
To get a better understanding on how the UI works and familiarize yourself with the game's input controls, you can visit the "Interface" page on this guide. What you can at least do is move around to familiarize yourself how it responds to your input and get you accustomed in getting in and around the place.
There are several things to see in front of the school. A wide assortment of weapons can be found there - which you might want to check and try. If you're into violent stuff, there are students on the farther right side of the campus to try the weapons with. Some "more" obvious weapons like the katana, gun, spear, and knives provoke the students - which would in turn make them try to attack you. You won't die from their attacks but you'll be neutralize and unhanded with your currently equipped weapon. Other non-obvious weapons like the magical cat hat, hammer, pick-axe, and bat would not create any provocations so you won't get any violent reactions. Nonetheless, when you use them against NPCs, it will still kill them.
If you are not much into killing, you can simply try to approach the NPCs and try to engage on a conversation instead. Mind you though that there isn't much to do with them when it comes to trying a conversation (probably still being worked on?). You can also enter the school building itself and amuse yourself with all the details you'll find there. In the school campus alone, you can check out the classrooms, the library, the soccer field, the pool, the offices, and the rooftop.
If you're done roaming around, you might want to head left of where you started (game start) -- which would lead you to a car park. You can use any of the vehicles there by simply going near it, and pressing the "Y" button when the option pops-up. The pertaining controls on how to use the vehicle will show up on screen as soon as you ride the vehicle. You can use it to roam around and check the perimeter of the whole game world.
The things to see include a lot of business stalls, a public bath, a convenience store, a cafe, some residential areas, a creek / aqueduct, and many more. There are a few NPCs too and a cat that you can ask to follow you around when you try to walk around the neighborhood. If it starts to get boring, you might want to check the settings tab and fiddle around with the physics of the game - to spice things up a notch.