There is nothing written on the wiki on how to use it, could someone explain it to me?

its not exporting the item to the chest

Items stuck in output usually means that the adjacent container is full or doesn't accept items
Try replacing the chest.

thanks :)

Crafting Upgrade use internal inventory to craft items and export them into a connected inventory.
How it works:

1. By pressing Side Inventory Key (c in my case) and Right-Click, the inventory will open.
2. Red zone is for your recipe. Simple as that.
3. After you placed your recipe, the yellow button called Validate will help validate the recipe, if everything is correct, the result stack will appear inside the aqua/cyan box.
4. Additionally, you can set the export direction using buttons from green box. By default, the direction is set to Down. That means that crafted stack will be exported into inventory connected at the bottom.
   

It can work only with the items from the inventory where it is placed.
For instance, if placed into a Macerator that macerated only iron ore, it'll work only with iron ore dust. I.e. the output of the machine.

The most common use for this upgrade is Machine Buffer. Here is a setup:

Click to open