You can use items in battle to recover your health, stamina, Ki, or recovery. Sometimes there are quests with multiple scenarios and even more enemies. You can get items as quest rewards, gifts from NPCs, or just simply buying them from stores.
You can also "Mix" material items to create new items through the Mixing Shops available in Toki Toki City. After successfully mixing an item, you can now create it moving forward by selecting the recipe instead of selecting the ingredients manually.