Login in to Magento Admin.
Go to Product – Catalog – Select simple product OR Create new one. Fill up Basic details if you created new one.
After that open “Customizable Options” Toggle” > Click on “Add Option”. Fill up details like “Option Title” and select “Option Type”. After that below “Add Value” Button available click on that for add option values. Fill up Title, Price etc. that you need.
You can show your product front end side with option you selected.