How do I define a player who joined as a variable?

Simple question buy I'm new to coding, if I wanted to define a player who joined as a variable, so I can change aspects of them later, how would I do that?

Here is a good way!

game.Players.PlayerAdded:Connect(function(plr)
	print(plr .. "joined!") -- says that a player just joined
	local part = Instance.new("Part", plr.Character) -- adds a part to their character
	part.Name = "TestPart"
end)