Hello!
English isn't my native language (and I didn't really properly learn English), therefore I can only write rather simple statements:
"The Man in the High Castle" is set in a world where FDR was murdered in 1933. That is probably the POD of this novel. Germany and Japan won WWII in 1947. The novel is set in the year 1962. The USA are divided into three areas:
1)The PSA (Pacific States of America), a state dominated by the Japanese Empire.
2)The Rocky Mountain States, some kind of a neutral zone.
3)The entire eastern areas of the USA, which are now under controll of the German Reich.
That is the *Oracle-Universe*.
In the Oracle-Universe a mysterious author named Hawthorne Abendsen has written an alternate-history-novel describing a world where Germany and Japan lost WWII.
That is the *Abendsen-Universe*.
In the Oracle-Universe the Nazis have banned Abendsen's novel, but the Japanese are surprisingly more liberal, therefore the Japanese and Americans in the PSA can freely read this novel.
Regarding the Abendsen-Universe: It is not exactly our universe. In the Abendsen-Universe, WWII was completely different, too. Yes, Germany and Japan lost, but the USSR didn't become a superpower, and the two superpowers after the war are the United States and the British Empire.
Two persons from the Oracle-Universe eventually experience a trip into the Abendsen-Universe. Mister Tagomi (the Japanese trade-guy) returns to the Oracle-Universe after only a few minutes. And Julianna Frink probably stays in the Abendsen-Universe. Both persons experience this trip shortly after they questioned the oracle of the I Ging (an ancient Chinese oracle-book and a major theme throughout the novel) and got the same answer, some mysterious text about the "inner truth".
If I remember correctly, Hawthorne Abendsen didn't even know that the universe that he described in his novel truly exists. Julianna talks to him and he doesn't really trust her.