In very simple terms, ICANN oversees the things that go on in the background so that when you click on a banner ad or type in a URL, your browser takes you to the right location on the Internet and you see the content you anticipated seeing.
Two major developments have arisen from the shift in control to ICANN:
What's the upshot? While it seems evident that the .com domain will continue to predominate for the near future, the default status that it currently enjoys will likely be lost. For new business websites, .biz is intended to open up some of the crowded space. Certain country codes, notably .cc and .tv, have been made commercially available for uses beyond their geographic description, partly as new alternatives to .com. It remains to be seen how well this will work. As you begin the process of creating an Internet presence, do a little research and find out what TLDs are open to you, prioritize the TLDs in which you want to be found, and use those answers to help you arrive at your new domain name.