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Create a free website or build a blog with ease on WordPress.com. Dozens of free, customizable, mobile-ready designs and themes. Free hosting and support.
The technical side of it will be the same, no matter if choose com or org, but you'll have to pay a bit up front for the hosting if you don't use .com (I'd recommend that, once you start to become successful, you'll want to have more control than wordpress.com gives you, and you'll have to migrate anyhow.).
WordPress is web software you can use to create a beautiful website or blog. We like to say that WordPress is both free and priceless at the same time.
Wordpress.org is the site for the platform, i.e. Where you can download a copy of wordpress and set it up on your own computer. Your webhost will already have done that for you.