Apple have never confirmed that AirPods are water resistant but many of our friends have told us that AirPods and it's charging case survive water tests.
Yes, you can control the volume from the phone using the phone's volume buttons just like we do in case of any other headphones.
It is very very easy thanks to seamless integration, which Apple has done. All you have to do is to bring your AirPods case near to your iPhone and open the AirPods case. The moment you open the AirPods case, your iPhone will detect it and will give you prompt to connect like the side image. Tap the connect button and you are done. Your AirPods are connected with your iPhone and they are ready to use.
The AirPods will begin charging as soon as they are in the charging case. It does not make any difference, whether the case lid is open or close.
Look past their offbeat design and you'll find that Apple AirPods' compact size and high convenience factor are a winning combination.