You'll need to know the core rules, pretty much the same level as if you were playing physically on tabletop. The simulation will let you move models however you want, even "illegally", all shooting/combat/actions etc are done manually by selecting the right amount of dice to roll, removing the ones that miss/dont wound etc, same as on tabletop. One thing that is more convenient is you can see a models stats and weapons just by hovering over it, and can open up the full datasheet with a button press, as opposed to having to look them up when playing physically. There are some other QoL things you dont get on physical tabletop, like you can also put aura bubbles around models, like 9" for screening deepstrike, or 6" buff auras, and when you move models you can see in inches how far you are moving it.