As Ash says it depends what you already know and just what area you would like to know.
Even the very best website designers/developers dont know everything about websites.
A good place to start though is by learning HTML it is really easy and wont take long to get the basics from that alone you will be able to make your first web pages/site.
After that I would highly recommend learning CSS and a server-side language such as PHP or ASP.
These are some good sites to start your learning.
http://www.htmldog.com
http://www.w3schools.com
Once you have made a few pages or a site you will then need to get a host to put your sites files on so the world can access your creation.
If your unsure on anything just come and ask.
