When you add custom options to a product in Magento 2, you give your customers the opportunity to choose product options as to their needs without relying on the product attributes.
To configure product custom options in Magento 2:
1. Navigate to Catalog > Products and choose the product you'd like to configure customizable options for or Add New Product.
2. Scroll down to the Customizable Options section and press the Add Option button.
- Give the Option Title and Type.
- Check if you want this option to be Required.
Note: once you put a checkmark near the Magento 2 custom option, it will be obligatory to choose by a customer.
3. Set the Option Values.
- Give a Title to the value.
- Set the Price and Price Type.
Note: if you choose the Fixed option, the price of the variation will differ from the price of the base product by a fixed amount, and if the Percentage option, the price of the variation will correspondingly differ from the price of the base product by percentage.
4. Enter the SKU for each Magento custom option that will be added to the product SKU as a suffix.
5. Once you finish Save the product and check the customizable options on the storefront.
And if you go to the Shopping Cart, you will see the Magento custom options right under the product name.
As defined previously, you can configure the custom option not for all Magento 2 products since most of them are based on the attributes.