It is different from a blog post because it remains static and will be displayed in the navigation bar (in most themes). Almost everyone starts with an About Me page to introduce themselves to potential visitors. It could be something like this:
Hello: I’m a courier by day, an aspiring actor by night and this is my website. I live in Madrid, I have a dog named Juan and I love piña coladas (and getting caught in a downpour).
… or something like that:
XYZ Socks was founded in 1971, and has been producing quality socks for its customers ever since. Located in Gothan, the XYZ company has more than 2,000 employees and tries to help in any way it can to improve life in Gothan.
If you are new to WordPress you should go to your desktop to delete this page and create some new ones with your content. Have fun!