If adding a new Product Group (Category) you must add a new Sub Category before adding the new Products.

All 3 must have a unique codes for each entry.

Add a Product Group

Select on Products drop-down

Select on Product Groups

To create a new Product Group select on NEW from the top

Enter a Unique Code and the Description of the Group 

Then click SAVE at top. 

Click on the [+]  symbol at the start of the Product Group line and then click on the "magnifying glass"  (see below)  add a SubCategory as per above New - code & description.

**Magnifying Glass: 

Add a Product

Select on Products drop-down 

Select on Products

Select New from the to add the Product

Enter the details that you require (Unique Code and Descrition) and select Active

Then select on SAVE

To search for any products, select on the Show/find panel and type the code/description of product

See video here: