When you have a product that comes in multiple variations - such as size or color - you can apply options so customers can customize their purchase.
Adding an Option to a Product
From your Admin Area, navigate to Inventory > Products.
Click on the product you want to edit.
In the Basic Info section, click Select Options.
Click the arrow (>) beside an option category to expand the list of available options, then select the checkbox next to each option you want to add.
Click Apply. Your selected options are now listed next to the Options field.
Click Edit Options to remove or add more options. Click the blue Save button to save the options to your product.
I don't see the Option I want to use.
Below each option category in the dialog box, you can click Add New Option to add even more choices to the available list. If you want to add a whole new option category to the list, you can also scroll to the bottom of the list and click Add New Option Category.
To learn more about advanced option and option category settings, see the article Option Categories & Options.