In order to make the product button in POS to use stock in your warehouse, you need to create a corresponding warehouse product. These warehouse products are also used in recipes. The same warehouse product can be used in multiple recipes. For example, you only need to create one cucumber warehouse product and use the same warehouse product in multiple recipes.
You can create three different types of warehouse products, defined by the measurement unit
The measurement units are:
NOTE: The measurement unit cannot be changed after creating a warehouse product, so if you gave a product the wrong measurement unit, you need to make a new warehouse product
To create a warehouse product:

Mandatory information for warehouse products:
It is advised to also provide the following information :

Remember to link the created warehouse product to a sellable product and recipes.
The guides for that can be found here: