An SKU is a stock keeping unit.
It is unique per item being sold. Below we have listed some simple examples:
If you sell t-shirts and they are unisex one size fits all then it will have one SKU.
If you have male and female one size fits all then you will have 2 SKU's. One for the male shirt and one for the female shirt.
If you have small, medium, and large for both male and female shirts then you will need 6 SKU's. One for the small male and one for the small female and so on for the medium and the large as well.
SKU's can be product variations such as Size, Material, Colour etc.
When you add your SKU it asks for a title and identifier, the title is visible for your customers, where the identifier is shown in your stock management.
Here is an example of the SKU sections:
Make sure not to repeat your SKU code - Shopstar will not save your product then. Use a unique code each time.