I have a really good idea for social networking site, but don't have money to pay someone to build it...?

[Colanth]

You'll need to learn computer programming. Then you'll need to learn a few programming languages. Then you'll need to learn HTML (the content of the site) and CSS (the look of the site). If you really want to learn, start with http://www-old.oberon.ethz.ch/WirthPubl/AD.pdf - but don't expect to be working on the site by August. It will take you months to learn programming, a few more months each to learn Javascript, PHP and SQL (at least months - it can take years before you become a good programmer) and at least a month or two before you start creating good sites. That completely neglects the need for graphic design.

Expecting to be able to convert a "really good idea" into a working site in a month or two is like expecting to become a neurosurgeon in a month or two. It takes years of work for someone to learn enough, and get enough experience, to actually create some of those "simple" sites you see.

Your best bet - if you can add something to the project more than the initial idea (there are millions of "really great ideas" for sites out there) is to team up with someone who has the knowledge and experience to build the site.