Characters can have different pieces of equipment assigned to them.
The team, at the same time, has a list of items called the “Armory”.
Equipment items, simply apply specific effects on equipped that will be removed on unequipped:

For example, this dagger adds +1 to the Attack attribute.
Slots are simply identified by a tag assigned on the Equipment asset (check above). You can create as many tags as you like (Helmet, Boots, Gloves, etc…)
For example, you can duplicate an existing Slot tag and rename to “EQUIPSLOT.Helmet” and use that on some new helmet equipment.
In order for these new slots to appear on the UI you need to adjust your UI accordingly. They wont be automatically added.
Create a prefab variant of UIGameEquip, make sure you use this new prefab in the Core asset as explained in Core Prefabs.
As an example, lets add a new slot for helmets. Duplicate one of the existing UIEquipmentSlot.

Now on the UIEquipmentSlot component (of the new slot), assign your new Helmet tag

Your UI will need to be tweaked to accommodate this new slot and you should assign an appropriated icon.