A URL is simply a website’s “address”, the one the appears in the white bar at the top of your browser. As for pronunciation, some people say each initial separately (“you are ell“), and others pronounce it like a word (“earl“). Either is correct. OR you could impress your friends and call it a Uniform Resource Locator, which is what it stands for.
The URL for Blogging Basics 101 is http://www.bloggingbasics101.com because I own the domain name is the .com or .net (or .org, .me, etc.) of your blog. You can buy a domain name for your blog at GoDaddy for about $10/year. If you haven’t bought a domain name and are using a blogging platform like TypePad or Blogger, then your URL may look similar to this: http://yourblogname.typepad.com or http://yourblogname.blogspot.com.