How do I make it so when a certain player joins something happens to them?

I know some part of the script ~~~~~~~~~~~~~~~~~ function onPlayerEnter:connect

I think XD

The event you are looking for is PlayerAdded:

Names = {"PlayerNameHere"}
game:GetService("Players").PlayerAdded:connect(function(Plr)
	wait(1/30)
	for _,v in next, Names do
		if v:lower() == Plr.Name:lower() then
			--Stuff happens here
			--Example: Plr.Character:BreakJoints()
		end
	end
end)

Use this example instead, it is more safer.

game.Players.PlayerAdded:connect(function(player)
	repeat wait() until player ~= nil
	-- code here :)
end)