Visual hierarchy is the way a page makes some things look more important than others. It guides the eye so people can see where to begin and what to notice next.
For example, a page title may be large, the main action may use a bright color, and supporting details may appear smaller below. It is like a poster that makes the event name easy to spot before the fine print.
If every item is equally bold, nothing stands out. A clear hierarchy helps people scan a page without having to read every part in order.