The Groceries tab is your shopping list. It holds everything you need to buy, whether you added it by hand or built it from a plan, and it is organized to make an actual shopping trip easy.
There are two ways in:
Lists you build from a plan land here too. See Building a grocery list from your plan.
Items are grouped by aisle, so produce sits with produce and dairy with dairy. Instead of zigzagging back across the store, you can work down the list in the order you actually walk it. How aisles are ordered is up to you. See Stores and aisle sections.
As you shop:
If you split your shopping across stores, store pills at the top let you filter the list by store. Tap a store to see just what you are buying there, then switch to the next. To set up which stores you shop, see Stores and aisle sections.
Tap into an item and a recipe strip shows which recipes it came from. That is handy when you are staring at "2 cups spinach" and want to remember whether it is for the soup, the salad, or both.
To manage the ingredients themselves, including aliases and default aisles, see Master Ingredients.