How to implement/design a website?

website designing, databases and etc are not my field. However, I have an idea and would like to implement it. In order to do so, I need to design a website which lets users log in and then they can post content to the webiste. Probably, they would have to use their credit cards for purchases too.

The way I see it is that I would have to have database to store profile info, contents posted by users. Also, some sort of mechanism to perform transactions. Also, I need a server which handles the client requests (probably in Java or etc).

I am familiar with some of the web languages but haven't done any project in that field. So my question is what are the languages I need to know? What is the easiest one? Where do I start? In general if you had to do the facebook how do you start?