how apps work iPhone 3G

http://manuals.info.apple.com/en_US/iphone_user_guide.pdf

An app is essentially what people used to call a "program" on a computer. Beyond that, it really is best if you read the manual linked by Stedman.

To stop music: Open the Music Application (App) then hit the pause button.

Another way to stop music is to double tap home button (square), slide to right, then hit the pause button.

Apps, once you close them by hitting the home button (square button) they are closed. But if you want to make them stop running in background, double hit the home button, then tap and hold on an app that pops up. It will go into jiggle mode, tape on the red minus button then it will stop running in background. Press the home button to get out of jiggle mode. But most people dont care about apps running in background.