There are two diffrent ways to pickup items. Directly to the inventory or through a loot window.
Click the Behavior buttton to modify trigger actions. When you created the item inside the item editor default trigger actions are added automatically. The Pickup trigger action allows you to pickup the items located in the ItemCollection to the defined window. Setting the Amount field to -1 will pickup all items located in the ItemCollection. You can also set the Amount to > 0 which will pickup the set amount of items.
It is also possible to pickup items through a loot window. Replace Pickup trigger action with ShowWindow. This will move all items to the defined loot window.