The idea is that you upload a picture to their server, and the server crawls on every websites and see if there are pictures that are similar to the one you upload. From those website you can find the source you want.
For example: I surf on the internet, and bump into a random girl's picture on a random website like this:
Remember, for this instance, the girl we are looking for the source is an asian, so focus on korean, chinese and japanese sites. First, how about taking a look at the first link?
How comfortably, I've bump into a chinese site(see that chrome's site translator? Chinese(Simplified Han). Now, I can't even understand what this site say, so I will just translate it. And...
Tada! Gotcha!"Monday beauty: South Korea's top car models Huang Mei-ji (Hwang Mi-Hee)". So what you need to do is Google her name(Hwang Mei-ji or Hwang Mi-Hee).
Now there are lots more potential that can be done with this engine. You can almost find the source for everything except those that aren't posted anywhere. Well, at that point, you will need someone to find it for you.
Remember, using Tineye needs you to work with both adaption and common sense. Be wise when looking for the source.