WordPress started in 2003 with a single bit of code to enhance the typography of everyday writing and with fewer users than you can count on your fingers and toes. Since then it has grown to be the largest self-hosted blogging tool in the world, used on millions of sites and seen by tens of millions of people every day.
WordPress started as just a blogging system, but has evolved to be used as full content management system and so much more through the thousands of plugins and widgets and themes, WordPress is limited only by your imagination. (And tech chops.)
In addition to online resources like the forums and mailing lists a great way to get involved with WordPress is to attend or volunteer at a WordCamp, which are free or low-cost events that happen all around the world to gather and educate WordPress users, organized by WordPress users. Check out the website, there might be a WordCamp near you.