So you already added an ingredient and want to link it to your invoices. This is relatively easy.
On the Ingredient Tab:
1. Create the name and set the yield factor for your recipe.
2. Pick Option 1: Link To Vendor
3. Select the Vendor and then select the ingredient.
What linking does: Anytime a new invoice with the same item number is added your ingredients price will update. This effects the cost margins on every single recipe.