CartGenie makes it super easy to link your customers directly to a specific product variant.
To create a variant specific URL, simply go to your product and select the variant options you want to use (example: Size: Small; Color: Red).
Then, copy the URL in your website browser.
You should see something like this after your primary product slug:
?variant=blue-small-fitted
Each variant option selected is added to the URL separated by a hyphen.