can u help me?

Do you mean adding new recipes? If so, then you would do that in the customization portion of the script itself. Like below line 35, you could add the line:
3 => [ [1,2,1] , [ [1,1,2] ] ],
Which would create a recipe for making the second weapon in the database, by using two of the first weapons in the database. (It's confusing at first, but it gets easier with practice).

And to delete recipes, just erase their line from the script.

Im having a problem with line 136
i get this error when i select crafting from the ingame menu:

Script 'Basic Recipe Crafting' line 136: NoMethodError occured.
undefined method 'values' for nil:NilClass

Its probably realy simple to fix but im just not following
any help would be well appreciated

I can imagine that problem arising from loading a save file that was created before the script was put into the project. Does it happen on a new game?

Works fine on a new save file. Thank You!