The very first clue you're going to want to follow is the domain.
A domain is the part of the URL that specifies what exactly that site is part of (institution, government, business, etc.).
Type in your email address to one of these people-specific search engines and if it's been publicly shared, it's going to show up in the search results.
Finding someone's email address is not usually accomplished with just one search unless the person you're looking for has put their email address on the Web somewhere.
The best way to find someone's email address is to start with a wide search and then gradually narrow it down using a variety of search tools.
If you're not sure who that email address belongs to, simply email them a polite message asking for their information - it couldn't hurt to try, anyway.
IP address: An IP address is a series of unique numbers that identifies a computer connected to the Internet.
Using the Deep, or Invisible, Web (the vast part of the Web that doesn't necessarily show up in a rudimentary Web search) to find information related to an email address can reap some impressive results.