How can I make a website like Facebook?

[Lindsay G]

You would likely design using php. ajax/javascript (possibly ruby on rails) and use a mysql database.

There is, however, no real need to develop one from scratch. You can use an open source solution such as drupal or buddy press to get you started. They start out the the functionality for user memberships, logins, etc.. then from there you can build off of that for a completely custom and unique social media website.