I'll get straight to it.
First, create an event. You can name it anything, but for simplicity I chose "Crafting Bench".
If you want to you can add a message in the first page of the event that says something like "This is a crafting table".
Now create another event page, and put a check in the "item exists" box. Pick the first item that the user will use to craft. If you want to, create a message that says "[item] placed on table". Now set it to turn a switch on.
Create a third page and check "switch _ is on" box. Select the switch that you set the first item to turn on. Now check the "item exists" box and select the second item the user will use to craft. Turn a second switch on.
Create a fourth and final page, and check both "switch _ is on" boxes. Choose the switches that you used for the crafting items. Now, use Change Items and decrease the amount of whatever item the player is using by 1. Do the same for the second item. Then increase the player's amount of the item they crafted by 1. Lastly, turn off all switches that the items turned on.
Set all page's priority to same as characters, and make sure they are all activated by the action button.
That's pretty much it. The attachment explains it better than I did. Also, in the example you should use the chest to get the items used for crafting. This system can be used to make items with more than two ingredients and the modifications should be easy to figure out. If not, tell me and I'll outline it for you.