Step #1: Go to Products and click on Add Product >> as shown below:
Step #2: Required fields will be indicated in red: these fields must be populated before you may Continue. If you exit this view by clicking << Back to Products, the information you enter here will not be saved: that will only occur once you hit Continue and move into the product creation process.
Step #3: Proceed through the tabs to input the relevant product data. A few notes:
If any required fields are missing data, a prompt will instruct you to address those before proceeding.
(Note: the product import function will be released soon. In the meantime, you can upload products in Shopify Admin.)