I’ve gotten a few questions about the difference between WordPress.org and WordPress.com. WordPress is blogging software and it comes in two main flavors. .Org is the place to go to download the free WordPress software to run on your own server. In this flavor you can modify the code (php and modules built using other languages) and install thirdparty plugins, themes, and other goodies.
WordPress.com is where you go to start and run a free online blog. Here you have a bit less customization available but you also avoid the headaches of hosting and maintaining the software on your own server. For beginners, WordPress.com is probably the place to start. Read more at WordPress.com.