AWS is far from simple, and there is a lot to learn. For a start, you will need to know what a Region and Availability zone are: http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-reg...

Roughly speaking: A region is a geographic location (e.g. eu-west-1 is in Ireland and eu-central-1 is in Frankfurt, Germany) The "Availability Zones" are separate datacenter buildings in that region connected by fat pipes.

For fault-tolerance, it is common to make sure that all of app's parts run across multiple availability zones in the region. This will happen without much manual config.

Crossing regions is very different - it's not going to happen automatically, they're pretty much isolated from each other. Only a few extremely-highly-available apps (e.g. netflix) have engineered to cross regions. See https://www.infoq.com/presentations/netflix-failure-multiple...