How to completing stocktakes and adding in new stock to inventory

Hi everyone,

 

I'm new to this.

The stock is the ingredients for bubble tea. I can't automatically update the stock levels as I sell drinks because the ingredients get used up making the drinks.

How do I complete stocktakes and enter in new stock level every two weeks? New stock is purchased during the month - how do I add in the new stock to inventory?

 

Much appreciated for your help.