To add a weapon in a slot, drag a weapon's prefab there.
Read there how to use Fist Attack.
If there is more than one weapon in a slot, you can switch it during the game. Thus, it is possible to group weapons by types (for example, the first slot has pistols, the second has machines, etc.)
In the "Health Slot" and "Ammo Slot" will be added ammo and first aid kits that you pick up during the game.
The "Ammo Slot" displays a count of ammo for the weapon that is currently selected in the inventory.
If you have ammo in inventory that is suitable for several types of weapons – they will be displayed in all of them, but after you use this ammunition with one gun, they will be deleted in other weapons.