There are several built in widgets available. A widget is a small block usually site related content that can be placed anywhere on a page. Normally, these are things that appear in the sidebars but you can place them in a page or post as well.

If you visit this page more that 3 times, there will be a highlighted section below. Nothing until then.

The RSS feed widget lets you show the most recent posts from any RSS or atom feed. This one is from Adafruit

This all appears all the time