Every WordPress theme can be customized by modifying its files, but many themes come with built-in options that allow you to make modifications without having to know any code or altering its files.
Depending on the theme, there may be just a few options or there may be a lot of them. However, it is essential to understand that not every theme comes with options.
Theme options are adjusted from the main administration page of your WordPress site. For example, Twenty Eleven, a free WordPress default theme, has a number of simple options but the default WordPress theme Twenty Twelve does not.
Note: The way to access your theme options depends on the theme. Some themes use custom additions to the lefthand column of your administration page while others require you to click on “Appearance” and then click “Customize” just below “Themes.”
Depending on how a WordPress theme is coded, the way that theme options can be customized can be via a visual drag and drop interface, radio buttons, checkboxes, or a combination thereof. Some themes have multiple pages of theme options, giving you very fine control over how your theme is displayed on your WordPress site.
And while theme options make it a lot easier for site administrators to customize the way that the theme displays, coding these options is a lot of work for developers. That’s why many themes have very simple theme options or none at all.