how do we really know if the stuff in the S.S book is really real.we don't know because we wasn't there
Most of it is true. Resercher and other have worked many years and by using technonly and other eveidence have figured out how people lived and ect. So don't worry about the accuracy. What they teach you in school is pretty much right.
There are no absolute truths; just evidence. For example how do you know your parents are actually your real parents?
You weigh the evidence.