Go to Products >Products section in the admin panel. In the add/edit products form, select the Options & Variants tab.
Choose the Option Set from the drop-down. You can import the selected option set or add your own set of options.
You can create variants to your product either manually or automatically. If you want to generate the variants manually, click on the Add New Variant Manually and enter all the basic details of variants like editing the SKU, weight, price, compare price, tag etc. for the variants. Clicking on Automatically Generate Variants will automatically generate variants for you based on the options that you have created.
Now, click on save to save all the details.
To view the product on the Storefront, click on the ellipsis button of the product and choose View Product from the drop-down.