You use a URL or "uniform resource locator" every time you open a website, send an email, or download a file. URLs are very important that without the use of this addressing scheme, it will be very hard for ordinary users to use the Internet and all its services.
We normally call URLs as web address, which is in fact, the perfect description of what URLs do. Valid URLs point to a particular file which could be a webpage, picture, or game, which an internet user wants to access. URLs must be unique for them to work, just like the way that our home address or phone numbers are unique.
An example of a URL is http://www.example.com/photos/mypic1.jpg. This address points to a picture that can be found online. Let's try to breakdown the address so we'll know more about how URLs are constructed and how they work.
http is the protocol and it defines the kind of service that you are trying to access from the web. Other web protocols are https, mailto, and others. The protocol part is always followed by a colon (:) and two forward slashes (//).
www is the server name and in this case it refers to a server that is located in the World Wide Web. Other server types that you will often see are ftp, smtp, gopher, and others. A dot (.) separates the server name from the next part of the URL.
example.com is the domain name and points to the destination of the URL. The domain name must be unique for the entire URL to work. Writing the domain name is not case sensitive so example.com and EXAMPLE.COM are the same.
/photos/mypic1.jpg points to the path of the requested page or image within the server.
Typing the sample URL above into your browser's address bar will instruct your computer to connect to the website called example.com which is located in the World Wide Web and access the picture from the folder specified in the address. The internet maintains a directory, called DNS servers, to help your computer find where exactly in the Internet is the site located.