Player State is for information about a player that you want to keep even when your player dies or disconnects, for example, level, maybe weapons, score, deaths, wins, playername, etc. I wouldn’t put health or mana in the playerState since those aren’t really persistent values in most games, but maybe in your game you want to have a health history or something, so that’s your call.
As for using the player state you don’t cast to Player State from Player Controller, the Player Controller already has a reference to the Player State you just type Get Player State in the search box and that variable should pop up, you do need to cast it to your own player state class though.