There are two ways to add ingredients. You can either link them to vendor invoices or create your own manual ingredient.
Name: The name of the ingredient.
Yield %: The amount of usable ingredient when cooking the ingredient. This can effect the price in recipes. Lets say only 80% of an egg is usable. That translates into paying more for eggs since you have to make up for the non usable part of the egg.
Option 1: Link To Vendor:
This method make sure that every time this invoice is scanned the price of the ingredient gets updated as well.
Select the vendor that the ingredient belongs to. Once the vendor is selected just select the line item in the drop down box.
Option 2: Manual Ingredient
This method lets you just add in an ingredient that is not linked to any invoice. You can go back and edit the ingredient at a later time.
Why would you use a manual ingredient? Lets say you want to create a recipe and the item has not yet appeared on an invoice. This lets you enter it in now to cost out recipes and link it later when you actually have invoiced this ingredient.