What is a blog? A blog is an "online journal" or "web log". It's a place online where you can post whatever you want using an easy content management system such as WordPress. In the days before Facebook, Instagram, and SnapChat, blogs were one of the best ways that a person could share personal stuff online with many people. Nowadays blogging seems antiquated and probably unnecessary. Just put it on Facebook! Or Instagram!
But do you need a blog? It depends on whether you have a lot going on that you want to communicate about, and a reason for communicating it. These days you may be better served with Instagram, Twitter, or Facebook.
If you're going to create a blog, be sure to put content into it on a regular basis. That's the problem with most blogs (including my own blog!). The content on them gets old fast. Personally, I just don't have time to update my blog every day or every week, so sometimes I'll find, to my chagrin, that months have gone by since I posted anything. And you'll need to update the basic WordPress software periodically, or the site will get hacked. They make it easy to update it, just don't forget to do it! I know of one guy who hasn't updated his blog since 2005. Yeah, really.
And when you do post things to your blog, make sure that you have a plugin in place (such as "WP2Social Auto Publish") to post your blog post over on your Facebook and Instagram pages, so people who check their FB or Instagram incessantly will realize you've posted something more permanent over on your blog and will click over to your blog to find out what it is.
To see why you shouldn't use WordPress to build a business website that you need to rank well in Google, here's an article I wrote on my blog about "Why I don't use WordPress to build commercial websites."
Note: This page you are reading used to contain detailed instructions on writing a blog in .xml -- there's no need for that nowadays. Just use WordPress. Or if you like a real technical challenge, try building a blog using Joomla. Both provide adequate "content management software" for creating a basic website; they are not only for blogs. Of the two, WordPress is way easier, although there's still a steep learning curve to become proficient with WordPress.