biography - Show more not tell implementation in writing?

What does this mean? If I have to SHOW more about a particular traumatic event which happened to me, I would probably not be able to recall the chain of events because I was in a panicked state of mind at the time of incident and there were just too many things happening around and all the people experiencing a lot of emotions which is firstly difficult to understand and then remembering them till we note them down in our journal. But keeping in mind, there are so many autobiographies that are published with so much detail and full of show, not tell events. Do authors/writers actually focus on some particular details of their everyday life? If yes, which parts? I have read a question which is similar(Writing techniques or exercises to improve ability to show rather than tell?) and it has some great tips but I still feel it doesn't answer my question. This is to ask about the art of observing/perceiving things so they would come naturally to me while I describe an event without forget the details.