Asking how to do an inventory is a rather difficult thing to explain without knowing how you want it to work and many other details. The most basic inventory system would consist of an array and having it store some sort of record of the item(s) in it. You may want to start with something that is more simple so you can get an idea of certin concepts that will be required to create an rpg.
Another idea may be to create a completly seperate test program that you can mess around with to figure out how you want to make your inventory system. Maybe some sort of array/record handling program that can give you a grasp of handling an inventory.