When creating a product make sure that the product has "Included in Online Store" toggle on. Variants are only available for products included in the store and cannot be used in order forms.
Scroll down and look for Variants. Click on the "Add a Variant" button
Add a variant option and option value
Once the option value has been added you can add a variant image and option to change the price for each option value.
You can turn on inventory tracking to limit the items they can purchase.
