Most items on the Settings page are pretty self-explanatory.

Helpful hits are: 

MANAGE STORAGE LOCATIONS
REORDER – locations can be re-ordered in whatever sequence makes most sense to you. The Inventory on Hand page will be ordered the way you choose. Press Reorder, then drag the locations to your preferred order. Press Done when you’ve finished.

CIRCLES WITH THREE DOTS –
Edit – user defined locations can be edited. Fridge, Freezer and Pantry cannot.
Create Section – all locations can be split into sections. This is useful for freezers and other larger locations to make it easier to find products.
Remove – any storage location can be deleted. Note that this should not be done if there are products in that location.

NORMAL CREW SIZE – this is used to calculate the additional provisions needed for extended trips or additional crew (guests). It’s activated under Shopping List.

MANAGE SUBSCRIPTION – this connects you to Apple’s or Google’s subscriptions function so you can manage your subscriptions quickly and easily.