Will 1 setup of ios 9.0.2 work for both iphone and ipad?
I have an iphone 6 and an ipad 4.I want to install ios 9.0.2 in both of my devices.Will i have to download different setups for the two devices or the same setup will work for both?
You will need to download two updates, different devices (and different generations of each device) have their slightly different version of iOS.
It should be quicker to download the update directly on the device via Settings > General > Software Update, that should only download the actual update - doing the update via a computer's iTunes will download the whole iOS version. But whichever way you do it take a backup first, and copy purchases over to your computer's iTunes library (File > Devices > Transfer Purchases).
iOS 9 requires an up-to-date version of iTunes on your computer to be able to sync, if you haven't already done so you may want to check that your computer supports it : http://www.apple.com/itunes/download/