Hi, I'm writing an iPhone app in simulator/debug mode at the moment. I'd like to know, after I build it, where does the binary go? I want to send this file to my friend to show him what I'm doing so far.
Also, how do I package apps into .dmg files? That seems to be the better format to send app to other people?
by default, the built results are located in {Project Folder}/build/Debug (or Release if you build in that config). You can use the hdiutil command-line tool to generate a DMG of your app - have a look at its man page which is quite comprehensive.
Have you joined the iPhone Developer Program? If so you will need your friend's device ID to generate a provisioning profile. I recommend that you read Publishing Applications for Testing for more details.
Your binary files will be on {Project Folder}/build/, there you will have one directory for each of the possible options: Release/Debug and iphoneos/iphoneSimulator.
To create the DMG read Creating a .DMG.