How do I make it so it chooses a number 1, 2 or 3, and then does a different function...?

You're using math.random wrong

math.random only accepts two arguments, not three.

game.Players.PlayerAdded:connect(function(player)
    local randomNumber = math.random(1, 3)
    if randomNumber == 1 then
        --Code
    end
    if randomNumber == 2 then
        --Code
    end
end)

Refinements

Use elseif. Don't keep using if statements. This makes the script shorter and cleaner.

game.Players.PlayerAdded:connect(function(player)
	local randomNumber = math.random(1, 3)
	if randomNumber == 1 then
		--Code
	elseif randomNumber == 2 then
		--Code
	end
end)

Good Luck!

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