How can I put in a userId on a server script?

I am trying to add a "if" statement where when you if you have a gamepass, it gives you a overhead gui:

if game:GetService('MarketplaceService'):UserOwnsGamePassAsync(player, vipid) then
	vip.TextLabel.Text = player.Name .. " - VIP"
	local clonedgui3 = vip:Clone()
	clonedgui3.Parent = game.Workspace:WaitForChild(player.Name).Head
          end

What I need help with is how I can get the userid on a server side script

Im pretty new to lua so go easy on me plz :)