game.Players.PlayerAdded:Connect(function(plr) Instance.new("Tool",plr.Backpack) end)
Its most probably because the char didint load yet, so waiting for it should fix the issue (Tested In Studio)
game.Players.PlayerAdded:Connect(function(plr) repeat wait() until plr.Character Instance.new("Tool",plr.Backpack) end)
First, get your tool. Then name, or one of, the part "Handle". Then press the plus next to workspace and add a tool. Next, you put the part(s) in the tool. Finally, put the tool with the part(s) in "StarterPlayerPack".