In whatever folder you place your downloads into. Some people use "my documents/downloads" on their machines. For instance, if you are using Firefox as your browser, you would click on Tools, Options, then look to see where your downloads are defaulted too. You can modify that location at will ... jot it down so you might know for future times.
Yes! You may or may not lose 18 pounds, but you will surely lose at least 10 pounds. It all depends on how your body functions.
You can find more information about "18 pounds in 4 days" at sites like http://www.everydiet.org/diet/18-pounds-in-4-days and http://www.18in4.com/. Keep in mind, however, that "18 pounds in 4 days" is a rapid weight loss program. Weight loss of this speed is typically not considered safe or effective.