From the Products menu category, select Catalog. Then, on the catalog page, click +New Product.
On the top half of the new product page under the General tab, you'll see fields to specify a product name, description, available on date, shipping and tax categories.
For products which you want all of your customers to have access to when making orders, make sure to turn the Visible To All Accounts switch on.
At the bottom of the page, make sure to specify what type of product it is, and the applicable accounts (from your Chart of Accounts) for the product. This is especially important if you will be setting up an integration with an accounting app, e.g., QuickBooks Online, QuickBooks Desktop.
On the Product Details tab, you can specify a SKU, price, cost, weight and size attributes, lead time, and pack/size.
After filling in all of the relevant fields, just make sure to click Save. Or if you have chosen "use variants" from the Product Details tab and want to create an additional variant, click +New Variant from the Variants tab.