WordPress uses a universal system known as wp_options to store data values for core functions as well as plugins. If you modify an option in the Settings section, it’s processed and stored in the wp_options database table. Plugins usually operate in the same way, handing off settings and other information to wp_options for storage or retrieval.
Not everything in wp_options has a corresponding UI, though. What if you had reason to modify an API key a plugin is storing, but the plugin doesn’t give you a UI option to update it? Or maybe some information is being cached and you need to blast it out while you’re working on a new theme.
WordPress actually has a page where you can see everything in wp_options, as well as edit the values. (You can’t mess with serialized data, though. You would need to use open phpMyAdmin for that.) You can access it by visiting the following URL, replacing example.org with your own domain, of course:
Obviously, you should be careful with this. You could break some things in your WordPress installation if you don’t know what you’re doing. So if you don’t know what you’re doing, you should probably not be messing around with the values…