By definition, a domain name is simply a human readable form of an IP address. In function it is the destination that you type into a web browser in order to visit a website, such a www.google.com. Metaphorically, it is very similar to how you would scroll to a contact in your cell phone rather than manually dialing the person by entering their full phone number; the phone number would be an IP address and the saved contact would be a domain name. Always buy a domain with a reputable domain registrar.
If you’re looking to optimize your content with plugins like Yoast you’re better off signing up with Bluehost and building your website with the WordPress CMS. All these types of plugins are either completely free or have a free version so all you have to worry about is paying for your hosting plan. WordPress(.com) only allows Business and eCommerce users to add custom plugins to their site, which means you’ll need to pay at least $25 per month for the privilege. With Bluehost, you can do it even if you subscribe to the Basic $2.95 per month plan.