Steps to add new Product/Service:
Go to Items Section -> Product/Services.
Click on New Product Button.
Add the basic details like Name/unit of measurement.
Select "Yes" on enable inventory for this Product, if you are maintaining stock for the same.
Add HSN/SAC as per Product/Service/description and other if necessary.
Select the appropriate option ->"I sell this product" / "I Purchase this product" as per your requirement.
Note: Once you create a product it cannot be edited to service and vice versa.