To understand Communism, you read Karl Marx and other works. To Understand Capitalism, you read Adam Smith.
Who and what do I need to read to Understand Fascist Theory and philosophy?
I would say that one of the most authoritative sources would probably be "The Doctrine of Facism" from 1932 by Benito Mussolini and Giovanni Gentile. Mussolini does not need much introduction, but Gentile was a prominent Facist thinker and politician and is regarded as contributing much of the Facist ideology.