An HTML block allows adding text, images, and other media to course pages using HTML markup. It has a built-in editor for formatting and embedding videos, sounds, and other files. To add an HTML block, an instructor turns on editing, selects the HTML block from the add menu, and pastes or writes HTML code into the block's configuration page. For example, a search widget can be added by finding widget code online, copying it, and pasting into the HTML block before saving changes.