Everything you stock at a Field Location is one of three kinds. They look similar in the app, but they behave differently, so it helps to know which is which before you start.
Parts: consumable inventory. The items a Tech uses up on a job and issues to a property.
Tools: gear a Tech carries and uses but doesn't consume. Tools aren't issued to a property. When a Tech arrives at a location, they confirm the tools that should be there (see 3.4).
Equipment: gear left at a property for a while and picked back up later, like a dehumidifier on a job site. Rather than being issued, equipment is deployed to a property and recovered afterward (see 3.6 and 3.7). You can track where it all is from the web admin (see 2.11).
All three carry a minimum and maximum quantity, and any of them can be set to restock when a bin runs low. Each kind has its own tab on a location's detail page, and its own view in the mobile app.
Note
Any of the three can either be picked from the Sibi catalog or added on the spot, by photo or from a receipt, when the item isn't in the catalog yet. Either way, it behaves the same once it's in.