Sale without a stock number

First you need to select "Retail Menu", just like the image below.

then once you have done that select the "New Sale", like the image below.

Then you are on the "New Sale Page", The up the top right hand corner you will see "Stock with out stock no item" Click on that,
Then this popup will appear

Then enter your details, then Press "Save", then you have entered a Stock item that doesnt have a stock Number.