how do I check how many players there are in game? using scripts

This is pretty easy, you get the children of players and then get the table size by putting a '#' for it

function GetPlayers()
    return #game.Players:GetPlayers()
end

while wait(1) do
    local Players = GetPlayers()
end

If you have questions or I made a typo, just ask

(You can also count them, but this way is easier, if you want for example to only count players with a value inside them named 'InGame' you can do things like this)

function GetPlayers()
    local Players = {}
    for i,v in pairs(game.Players:GetPlayers()) do
        if v:FindFirstChild('InGame') and v:FindFirstChild('InGame').Value then
            table.insert(Players, v)
        end
    end
    return #Players
end

while wait(1) do
    local Players = GetPlayers()
end