What is the function of Google's 'I'm feeling lucky' button?

The "I'm Feeling Lucky" tab on google is just a faster way to find the thing you're looking for. For example: if you type, "Miley Cyrus pictures" and click "I'm Feeling Lucky", google will then go to the best page to find what you're looking for. So in this case, you would get the best web page for finding good Miley Cyrus pictures.

That is how the "I'm Feeling Lucky" tab works.