Your party inventory is visible by anyone in the party. It is useful to keep items or loot in here that have not been divided up or claimed yet. When items are in the party inventory, your whole group has access to them. Anyone can view, edit, sell, or transfer the item out of the party inventory. This makes it really simple to divvy items up after looting. Anything sold from here will deposit funds into the Party Wealth.
Click the blue "View Inventory" button in the panel to see the full view of all items and containers. Use the green "Add Item" or "Quick-add Multiple Items" buttons to add items from your Party Info screen. This can also be done in the main inventory screen.
The quick-add modal is a condensed form that allows you to record up to five items at once. This is useful if the GM is reading loot quickly, and you want to add items to identify later.
For more in depth information about managing an inventory and items, see the Items & Inventory section of the guide.