Instead of endlessly typing an answer and posting photos, I will give you links to everything you want to know about dragonflies. I have photographed several species over the years. Also, I wrote an article on the "Widow Skimmer Dragonfly" which is among my HubPages articles. You can read that if you want to but all information on dragonflies that you require can be found on the websites listed below. If you have other nature questions then feel free to contact me.
The Dragonfly Site - Best Dragonfly Information Resource Online
21 Facts.com - Interesting Facts About Dragonflies
The Dragonfy Website