The icon widget lets you add icons to text fields or labels. Select the icon widget and drag it to your canvas to a location where a green line appears, this means you can place a icon there. It can not be dropped directly onto the canvas but needs to be within at least an "active" element (like a Rich Text element).
When you add an icon a movable menu pops up with the different icons available in the modeler where you can choose the icon you want. This menu can be navigated with the use of arrow-keys and the tab-key and has your recently used icons in a separate section at the top.
When an icon is selected the following options appear in the properties pane:
Icon: Change the used icons by selecting the flag and selecting another icon from the menu or type the technical name in the icon box.
Appearance Style: Select a color from the template colors. Size: Size of icon in number of pixels