Usage: {{IconLink|Flourish Icon.png|Flourish}}
Result: 
Flourish
The link text can be changed with a third parameter:
Usage: {{IconLink|Flourish Icon.png|Flourish|Custom Text}}
Result: Custom Text
The default size is x40px meaning the icon is scaled until the height is 40 px. It's usually important to limit the height since the icons are used inline, and a very high inline image makes for an unpleasant text layout.
An alternative value for the height can be provided:
Usage: {{IconLink|Flourish Icon.png|Flourish|size=25}}
Result: Flourish
Usage: {{IconLink|Flourish Icon.png|Flourish|Custom Text|size=25}}
Result: Custom Text