How to do Item Fusion?

Materials:

You need 5 pieces of a specific item before you can fuse them. Click on the potion icon ("Materials," at the top of the screen).

From there you can fuse materials. Click on the specific materials you want to fuse. A small window will appear showing the description of the item and the cost of the fusion. Click on the "Material Fusion" button and that should be able to fuse the materials. If you have 50 materials, you can fuse 10 sets to save time.

Equipment:
 * You must have two items upgraded to +9 at the same category and tier. (Two 3-star hats, two 2-star armors, two 5-star pets, etc.)
 * The rarity does not matter. The result has random rarity and no upgrade bonus.  Fusing two "Unique" items has the exact same outcome as fusing two "Normal" items.
 * You can fuse 5-star items into 6-star items, but you need three +9 items to do so. The result has the same basic stats as the first item you chose, but it can be upgraded beyond +9.
 * If you fuse two items with the same name, you will not be more likely to get a higher-tier version of that item. Example: Fusing two 4-star Orc pets will not usually give you a 5-star Orc.
 * Fusing two female items gets you a new female item. Fusing two male items gets you a male item.  Fusing two items that are limited to the same character will get you an item for that character.  (You can fuse two Kid hats to get a better Kid hat, for example).
 * If the items are different, you are 20% more likely to get an item resembling the first item you choose. If you choose a female item first, then a male item second, you are 20% more likely to get a female item.  If you choose a Khan item first, then something else, you are 20% more likely to get a Khan item.