URL is a Universal Resource Locator. The URL is the address that you use to get a web page. It contains the domain name and may have more information that points to a specific web page.
In its simplest format a URL is the protocol being used and the specific server at a domain and the domain name. The URL to my web site is http://www.dwightwatt.com Letís look at what that tells the machine.
First it says it is using the HyperText Transfer Protocol (HTTP) that is the basic protocol (rules) that web pages use. Since normally we are using HTTP or HTTPS (the secure version) the browsers (IE, Chrome, Firefox, etc.) will assume we are using HTTP if we do not enter that part.
The next item is www. This is the name of the server (large storage computer to serve web pages to us) and is normally www but can be different particularly if an organization puts parts of their pages on different machines. Again, the browser will assume the www as the server name if it is left off since that is normal naming practice for web servers. WWW stands for World Wide Web).
Then comes the domain name, in my case dwightwatt.com This is the specific name I own for my web pages. The dwightwatt is the name I chose from those available and the com to indicate it is a commercial or normal use type page. With the exceptions of .edu and .gov pretty much you can choose which ever type of last name. Other popular top level domains are .org and .net. Originally the intent was .org was non-profit groups and .net was network providers, but they are used more widely now for all types. There are lots of other last names available. The Internet authorities keep tight reins on use of .edu and .gov and you must be special approved for them
In some cases, the URL may include additional information to point to a specific page instead of the general opening page for the web site. For instance if you wanted to go to the paintings page on my web site you could go to www.dwightwatt.com and then click links to that page or you could use the URL of http://www.dwightwatt.com/dwatt/paintings.html While writing this I realize I need to add two paintings I did in the last year and that is always a problem of web sites of keeping them current. This URL says I have a folder called dwatt on my site and in it is the file (paintins.html) that shows links to my paintings. This page is still essentially as when I first did the web site in 1997.