This is a sample page. It is different from posts because it always stays in the same place and (with most themes) is displayed in the website navigation. Most start with an imprint, privacy policy or an "about us" page to introduce themselves to potential visitors of the website. It could say, for example:

Hello! By day I work as a bicycle courier, by night I'm an aspiring actor and this here is my website. I live in Berlin, have a big dog called Jack, like piña coladas but less being left out in the rain (without an umbrella).

...or something like this:

The XYZ company was founded in 1971 and has been providing the public with high-quality products ever since. At its location in a small metropolitan city, the company employs over 2,000 people and supports city residents in many ways.

As a new WordPress user, you should go to your dashboard to delete this page and create new pages and posts for your website. Have fun!