How do I make the script choose a random player?

You can use :GetPlayers() to get a table of players and then use math.random(smallestNumber, biggestNumber) to pick a random player in that table.

# means number of items. if you say print(#players) you are printing out the number of players.

here's what the code would look like:

players = game.Players:GetPlayers()
randomPlayer = players[math.random(1,#players)]

keep in mind, if you try running this in a script immediately like this, there won't be any players and you'll get the error: bad argument #2 to 'random' (interval is empty) so make sure you're using the code above when there's actual players in game.