This is a text widget, which allows you to add text or HTML to your sidebar. You can use them to display text, links, images, HTML, or a combination of these. Edit them in the Widget section of the Customizer.
This is an example of an about page. Unlike posts, pages are better suited for more timeless content that you want to be easily accessible, like your About or Contact information. Click the Edit link to make changes to this page or add another page.