How can i make this plugin?

Hi,
i'm making plugin that can upgrade item
so if we open inventory(with inventory key)

and get some special item(has item meta) and click that to make it go to my cursor, and click that item to what we want to upgrade.
-> this means load cursor one item and click that item to what i want to upgrade

how can i code this?
it might use InventoryClickEvent
but i don't know how can i code it.

 

Inventory key?

 

i think that he means when you open the inventory it first check if you have the "specific key" to acces the inventory,,not really sure buy thats what i think

 

I'm pretty sure he means "Inventory key" as in the E key, to open your local inventory.

Here's my suggestion: