WordPress.com is a free blog hosting service. You can create your own blog even if you don’t have a hosting provider. The blogging software of WordPress.com is also free but you can only use it through web interface.
This means you cannot download the software and install it on your local server. You have to log-in to your account in order to blog.
WordPress.com has some plug-ins and functionalities disabled. You need to upgrade to premium membership to get all the premium services. Rewriting codes and creating a personalized plug-in are also not allowed in WordPress.com free services.
WordPress.org, on the other hand, is an open source blogging application and offered for free. It is similar to its dot com counterpart in appearance and features. However, you can download the WordPress software in dot org. It can be installed on a local server or on paid hosting.
You can do anything with it including creating your own themes, templates, plug-ins, and other functionalities. The source codes of the software will be available to you so you can reengineer it to suit your own blogging needs. You can then share it with the network so other bloggers can utilize your plug-ins or themes.
Blogging at WordPress.com is ideal for everyone, whether you’re a novice or advanced blogger. In using WordPress.org software, you need to know the basics of configuring the application on a local server, so it is generally ideal for bloggers with more experience.