Your Dinoz has a certain amount of available slots which he can fill with combat gear. Some items can be equipped for use in fights.
To equip an item for battle, use the Inventory tab. The action equip is only available for certain items. Once an item is equipped, you may remove it by clicking it's slot in the equipment.
Most of the battle items can only be used once. This means that once your Dinoz has used an item during a fight, it will be destroyed - freeing up the slot for new items.
Combat gear allows you to adapt your strategy to the monsters you encounter. Use these items wisely.