The equipment interface lets you view and manage the items in your inventory, especially equippable items. You have a number of slots in which to put things.
Fast-Use: These are slots for usable items that you may want to make use of in combat, particularly, or otherwise have readily available. Otherwise, you have to rummage in your backpack or other storage option, which is not really combat-suitable.
Equipped: This lists the various items you are currently wearing and where. In many cases, you can wear items over other items, though the effectiveness and usefulness of doing so may depend on your strength, and sufficiently bulky and inflexible items can't have other things worn over them and will slow you down. For example, you can wear more than one suit of chainmail (though it's mostly heavy and impractical compared to a suit of plate armor), but you can't wear two suits of plate armor over each other.
Equippables have:
Coverage area: What parts of the body it covers.
Coverage degree: How well it covers. (A ring covers a very tiny portion of one finger, for example, whereas a pair of gloves covers both entire hands.)
Durability: How sturdy it is (its hit points, basically).
Resistance: How resistant to damage it is.
Transference: How much blunt force transfers through to the wearer.
other stuff…