jailbreak in iphone

how to jailbreak?
Too long to answer you here, you may read it here: www.iphonehacks.com, and follow the detailed instructions how to do it.
After JB, you will find a new app called cydia. It is an alternative to AppStore of apple. It is another source of appz for you. Includes lots of free applciations, and some apple not approved application, like using bluetooth to transfer files, using Wifi to connect with itunes etc.