Action RPG Inventory System

I have a few questions.

  1. How do I get information how much amount of an item is in the inventory.
  2. How do I get information which item is on which equip slot equipt.
    3 How do I remove items from inventory that are inside inventory current with amount.
    4 How do I add items to the inventory that is an default item?

Hope you can answer me those questions because I really need these functions.

Cheers,
Bander