I'm planning on building a classifieds website with an emphasis on its user community - something like ebayclassifieds.com but with a stronger focus on user profiles and with additional forums and user blogs. It should also be connected to social networks like Facebook or Twitter (so that you have the possibility to log in with those accounts or to automatically post links of your new ads to those networks).
My problem: I only know HTML, CSS, and a little bit of JavaScript and XML. I can do the design/framework, but I don't know how to make it work. Could anyone tell me what I need to learn to be able to do this? How do I start?
I know it sounds a little silly, but I'm not just doing it for the end result, but also for learning the technology.
Any suggestion will be appreciated!