How do I create slots for my inv system?

http://i.imgur.com/bWbonsy.png

My code for the inventory system is shown above. When I put a string into the text box it creates an object in the inventory or adds it to an existing stack. I am wondering how I would make it so that the items that I add to the inventory will be shown in slots and when I select a slot I would like to be able to discard the item.