The Uniform Resource Locator is used to locate documents and pages on the web.
The first part of the URL identifies the transfer protocol -- often HyperText Transfer Protocol (http://) or HyperText Transfer Protocol Secure (https://) -- which defines how messages are formatted and transmitted. It rarely needs to be specified in the URL any more.
The next section of the URL is the domain name, which indicates the owner of the page. SDSU's domain name is sdstate.edu. The .edu in the domain name indicates that it is an educational institution. There are many types of domains: .com, .org, .gov, etc.
The final part(s) of the URL are the path and file indicators. This indicates which folder and subfolders a particlar web page or document is located in so that it can be found and delivered to your browser.