Icon is a glyph (small image) used in place of short text on a page. For example, arrow icons can be used to indicate a direction, audio & video icons can represent common ways to interact with audio and video, etc. Click Edit to open the icon properties window (Content tab), then click on the icon placeholder. Wait for the icon library modal page to load. Select necessary icon.
To control the size, change the font-size and other properties of the icon, select the Style tab and make necessary edits.