How exactly does auto scaling in AWS work?

I read the docs but still didn't understand anything. The aws forum takes time to answer. Here is my scenario:

I had code in an ec2 instance but needed to join the instance to a scaling group. There was one already created so I just joined mine to that since it was "unused". In a moment notice my instance terminates and I lost all my code within the instance. Only the original instance from the scaling group maintained itself. Now my question: is scaling supoosed to help the same service performance? Because:

• the dinamically created instantes DO NOT posess the same adress.

This means I can SSH to one but if I SSH to another one will there be the same code?

• the dinamically created instantes DO NOT posess the same security group

• the original instance (that could hold the code) ALSO CLOSES if replaced by the new one (I don't know the criteria). So, the one holding the code can always close...

So, between trying to understand if need to try and recover my terminated ec2 instance and understanding all this process, I must admit I'm quite lost because nothing really inspires "merely incrementing process power" with confidence so I really don't know what to do...