How to transfer apps from iPhone to iTunes

Apple has made it ridiculously easy to transfer iPhone apps to iTunes. There are a couple of things that need to be in place first: 
Sign in with your Apple ID
 First, navigate to the “Store” menu entry in iTunes, and choose “Sign in” if you havenot already. This will need to be the Apple ID that you used when downloading the apps from your iPhone.
 Authorize computer
 Next, return to the “Store” menu in iTunes, and choose “Authorize Computer.” If you havenot yet done this, iTunes won’t let you transfer those apps. If you purchased apps with multiple accounts on your iPhone, then you will need to repeat these first two steps with each account. 
Transfer Purchases
 All that left to do is to connect your iPhone to your computer (via USB), and let iTunes do its thing. After backing up your iPhone, it will begin “transferring purchases” into iTunes. This includes both free and purchased apps — all will be backed up on your desktop or laptop. If you have previously synced your iPhone with another computer, you may see a box that says “your iPhone is synced with another iTunes library.” In this case, simply press “Transfer Purchases” and your apps will be copied. If iTunes doesnot automatically transfer your purchases, then you may have previously selected “don’t ask me again” when prompted about transferring purchases. Then simply right click on the name of your iPhone in iTunes. One of the options should be “Transfer purchases from your iPhone” Select this. 
Wi-Fi syncing
One last thing is to note that, starting with iOS 5, you can wirelessly transfer your apps from your iPhone to iTunes. In iTunes, the tab for your iPhone will have a box that says “sync with this iPhone over Wi-Fi.”
 Leave it checked, and your apps will be wirelessly copied to iTunes regularly. Leave it unchecked, and the syncing will only happen when you physically connect your iPhone to your PC.