There are many ways you can build websites, but the most useful language to learn when starting out is HTML (HyperText Markup Language). This is the basis for most websites and is pretty easy to learn and understand. Formatting the design of the HTML elements should be controlled by CSS (Cascading Style Sheets). For more advanced web developers there are a multitude of languages that can be used, including but not limited to Javascript, PHP, XML, ASP etc etc.
I am not going to teach you how to program a website here, as there are many websites out there that can teach you the technicalities of web design much better than I could possibly do in these pages, but I will put a few recommended Links for further reading.