I'm in a hurry so I'll respond to several posts at once here.
You do not need to download any app at all. Android Device Manager is already built into your phone and has been from the beginning (and is also on any current updated Android phone). You can set ADM settings in the Google Settings app and make sure it is checked under Device Administrators in your Security settings. You can then use it remotely by going to Device Manager while signed into your google account -
https://www.google.com/android/devicemanager - or by installing the ADM app on another phone and signing in under your account. You do not need the app on your phone - it is only needed if you want to use a different phone to find your phone, lock, or erase. Or just use the web browser link I posted above.
Now the kill switch part. There is no special setting for it. It is implemented automatically as long as you have a lock method set of the proper security level and you have a google account on your phone. That is why after the update you are prompted for a PIN to be set. You can remove your lock screen security and then the kill switch will be disabled. As long as a PIN/password/(possibly also pattern lock) is set and you have a google account associated with it, the kill switch will be turned on.
With the kill switch on, the user will need to know your google sign in info to be able to use the phone. If they factory reset it to get around the PIN or if your remotely factory reset it to wipe the data, then after the reset they will be prompted for your google username and password and will not be able to continue without signing into your account. With the kill switch off, they can factory reset and do whatever they want with the phone.
As far as India or other countries, if you have the same firmware installed that has the function then it should work the same.