Browse to pick stuff in this shop.

You can type the name of stuff in this shop or type the stuff's ID number to make the cursor jump to it.

You will see an indicator of whether each item is in-stock.
 * means infinite
 - means not in stock (or only
   present for sell rules)

Click the "+New" button to add new stuff.

Right-click for a pop-up menu that lets you choose if you want to "Pick" this stuff, or if you want to edit it.

Press CTRL+F or click "Filter" if you want to filter the list to only show stuff that matches a certain string of text.