WordPress History
WordPress is a content management system or (CMS) that was created in 2003 by Matt Mullenburg. WordPress is often used to create blogs but can also be used to make and design websites. WordPress is also an open source product which allows you to change WordPress for how you want to use it. WordPress is a popular tool for many websites as it requires the creator to know very little about coding.
WordPress.org Entity
WordPress.org is similar to a resource center as it provides WordPress software for downloading. It requires you however to independently find a hosting service, install WordPress and take care of maintenance alone. WordPress.org is self-hosted unlike WordPress.com. WordPress.org costs nothing to download the software however you will have to pay the domain and web hosting yearly. For WordPress.org you will need to have experience in customizing,maintenance, configuration and update as this is a self-hosting site. Custom themes can be installed on your site or you can create your own.
WordPress.com Entity
WordPress.com offers a managed hosting service that allows you to build a website using the downloaded WordPress software. WordPress.com costs nothing to create/launch your site unless you want to purchase a paid plan with more features. WordPress.com also provides built in hosting and is great for beginners as it has everything you need to build a site in one spot. There are several built in features that allow you to not need extra plugins as well. Many themes and custom options are availible in WordPress.com and more themes can be purchased or can be downloaded.
Summary
WordPress.com and WordPress.org are great tools for website creators. WordPRess.com and WordPress.org are easy for both beginners and more experienced people. Depending on what kind of hosting you want to do whether it is included in the download for you or you have to download it and self host it.