Html is "stateless", so the server never knows if you're logged on or not.
All server-side application frameworks have facilities for it. http://www.webdevelopersjournal.com/articles/logon/xml_jsp_logon.html for example tells you how to do it using JSP (Java server pages) if you've got a Java server running on your webserver. That Java server keeps track of session information.
I'm sure a .Net environment has comparable possibilities, but I never used them.
http://msdn.microsoft.com/en-us/library/ms178329.aspx is about ASP.Net (which is a rather old implementation of .Net).
And I'm sure students of mine have done it in PHP. Here are a few links I found:
So the first thing to do: ask them about their preferred webserver language: Java/JSP, .Net (several versions), PHP, ASP. Then implement that on their server (and possibly your own development environment) and start experimenting.
So here's the thing. I have created several websites so far, but using only HTML and CSS (and some open source scripts). However there is this firm that is willing to hire me, but they want me to create a website (2-3 pages are enough) that look different if you are or are not logged on. But I have never done anything like that and I don't know where to start. I'm not sure if HTML will do the trick or should I use PHP or ASP? And where is the login information stored? As a users in the DC or IIS where the website is hosted? Or in an SQL or some other database? The stupid thing is that they want to see it in a week (they don't want it to be looking good, only the code should be correct) and they will assign me on a project at March. I will be able to learn more then enough till then, but I need it now. If anyone can help in any way - guiding, linking to some useful information, etc. it will be greatly appreciated. I am willing even to share some (or most) of the first paycheck if someone give me a hand with the coding. After all it will be thanks to you I get hired in the first place.
Off to google for info.