Creating Secure Action Buttons + Keybinding them

[CrittenxD]

Hi, I am a noob at scripting and I'm struggling to create a secure action button so I can use something along the lines of UseContainerItem or UseItemByName. I also would like to use this button via a Keybind in the Key Bindings options.

I got some code which I tried to use on my keybind resulting in a popup saying that I'm trying to use a protected function:

function UseItem()
local a
local b
local s = 0
    while s <= 4 do
    local c = 1
    local n = GetContainerNumSlots(s)
	    while c <= n and n > 0 do
	    local r = GetContainerItemLink(s, c)             						
		if r then 
			local x = string.find(r, "%[") +1;
                        local y = string.find(r, "%]") -1;
                        local z = string.sub(r, x, y)
                        if useitemtable[z] then a = nil UseContainerItem(s, c) c = n s = 5
		        elseif questitemtable[z] then
				if not a then a = s b = c
				end
			end
	        end
            c = c + 1
	    end
    s = s + 1
    end
if a then UseContainerItem(a, b)
end
end

I think this will just use the first item it finds in the inventory that is in the set called useitemtable, if there is none it will use questitemtable. I just don't really understand how the button frame works at all, I think I have to use "item" type and the ["bag", "slot"] attribute in the button frame, but I have no idea how to actually use the button with a keybind or how exactly the button frame would look. I know I could just do a macro with /use, but there are roughly 20-30 items on each list so that just won't fit.