A highlight is the digital equivalent of swiping a yellow marker over a passage of text. Click the screencast to watch the creation of a highlight.
This introduction/ definition about highlighting does not give clear steps, it has the read watch a short clip on how to highlight text, but it never tells the reader how to actually do it. It assumes prior knowledge, for example that the reader must already know how to select the text they want highlighted, they also simplified the explanation the highlight isn't always yellow it can be different colors.