If you have an Android device, you'll (presumably) have a Google account. Your Gmail address will be [identity]@gmail.com. The whole point is to use it transparently, as I explained. The Gmail app will already be on your phone - look in the app drawer. You'll have signed into Google on your device, so the app will be working as soon as you open it - there's no setting up to do and it's very easy to use. Have a play with it and I suspect you'll be converted as quickly as I was :smileyhappy:
Sign-in before sending (or whatever it calls itself*) means that your device logs into your BT account to authenticate you before it tries to use the SMTP server. When you send over a BT connection, the network already knows who you are, so doen't need this. It needs authentication when you use another network to make sure you're a bone fide user and not a spam merchant. It's a long time since I set up the Android email client, so I can't remember the settings exactly, but there'd be an option in the Send settings somewhere, possibly a sub-menu.
* I think the word "authenticate" may come into it.
