A variant is a particular variation of a product (eg size, color) and has specific variant options (eg small, medium). A variant is always tied to price and/or inventory. You can also make combinations of variants options like Medium Blue.
As a first step, make sure to go to the Catalog Tab and click Variant. Create the different variants you need like Size (eg 6XS up to 6XL) and Color (eg blue, green, and yellow).
Next, open a product in the Catalog and assign the variants Size and Color for that product, along with all the options you need.
Move on to the inventory/price tab and enter the price on a product level. Next, click the “Generate variant options” to see the matrix of variant options with their respective SKU code, price and inventory.