Domain names are the names of web sites on the Internet. They are names like dwightwatt.com, cnn.com, gvtc.edu, and whitehouse.gov When we want to see a website we use the domain name to go to the web site.
The Internet has not always used domain names. Domain names were created and started to be used in the early 1990s. Prior to the early 1990s the only way to pull up material that an organization had on the Internet was to use their IP address (which the Internet actually converts domain names to and still uses). Then you had to type in a number like 192.168.13.1 to go to where I had my information stored. Obviously that did not work well for most people and the only ones who used the Internet were government, military, colleges and libraries and research organizations. You had to remember the IP address for any you wanted to contact.
With domain names we can use a word that the organization has bought that represents them. Domain names are sold by domain name companies and administered by international organizations set up by the US government and still highly influenced by them.
In front of the domain name, the name of the server the web page is on is named. Most often the server is called www, but if you watch when you go to web sites quite often that first part will change at the site as they have their pages on different servers.
The first part of the domain name tells us the specific organization such as dwightwatt or cnn. Domain names are not case sensitive so they can be upper or lower case. However, if there is folder or file information at the end after a slash (/) that is case sensitive. The last part of the domain name is supposed to tell us the type of organization but you can buy most extensions. A few are tightly controlled such as .mil (military), .gov (government) and .edu (accredited educational institutions, although initially accreditation was not required so there are a few grandfathered in.