As far as how they work, all you need is to present your E-ticket receipt (which should be provided to you by your TA or the carrier) as well as a personal ID upon check-in. If the carrier has a kiosk for self check-in, all you have to do is insert your credit card that you used to purchase your ticket and the machine will automatically print our your boarding pass. As far as changing flights go, it varies from carrier to carrier, routing to routing, fare rules to fare rules, etc.

I personally have found E-tickets to be more convenient and cheaper (no additional fees as oppose to a traditional paper ticket and no need to pay for the shipment of paper tickets).