@vaporeon_ very roughly: players take turns hitting the ball. if they're unable to hit it after a few tries, they miss their turn and their team gets an "out". if they hit it but someone on the other team catches it, the player who hits it has to leave and their team also gets an out.
while the ball is in play (in the air, or being passed around by different players) the player who hit it gets to run around the "diamond", marked by the place you hit the ball from and three white pads placed in a diamond shape, called "bases"
each base is like a checkpoint. if you get there, you're allowed to stop and be safe. you can run again the next time someone on your team hits the ball. but, there's a player from the other team at each base, and if they have the ball when you get there, your team gets an "out" and you have to leave
every time any player makes a full lap, all the way back to where they hit it from, their team gets a point
every time a team gets three outs, the team hitting the ball and the team trying to stop them switch places. when each team has had a turn in both positions, that's the end of an "inning", and the game ends after 9 innings (with extra overtime innings if they're still tied at that point)
@monorail @vaporeon_ this is close to correct but it still doesn't explain this:
https://www.youtube.com/watch?v=NbylTXlxvJg