How do i make a backpack gui that shows up when you press letter e?

I Have seen a script like a backpack but its already shown up. what i need is an backpack gui that when you press letter e it will show up and can be expanded when you use a bigger backpack

You need to use a KeyHandler system like this:

function onKeyPressed(key)
	key = string.lower(key)
	if string.byte(key) == 69 then -- If the key pressed is "E" then...
		-- Your code
	end
end