“Blackshirts and Reds” is a good introduction by Michael Parenti that explains in plain terms they “why” of communism and fascism. Parenti’s books tend to be in plain working-class American English, they’re well-sourced, readable and informative.

Frantz Fanon’s “The Wretched of the Earth” is a psychiatrist’s view of the Algerian revolution and gives a on-the-ground impression of the why and how of a socialist revolution from someone who lived it, in a book addressed to the colonized people of the global third world.

“The State and Revolution” by Lenin is a very short and readable explanation about why we need both.

I personally would recommend karl kautsky or emma goldmen.