Every file has a unique identification name or number, called a URL .
URLs work something like telephone numbers, broadcast frequencies, and call numbers of books in a library. In general, URLs are written without spaces in several parts separated by special punctuation. The first part of a URL, called the scheme , identifies the type of resource it is. The scheme identifies what Internet protocol is being linked. The next part of the URL is a code for domain name of the Web server where a file is located on the Internet.