Communism is a post-socialist society where class has been eradicated and all production and distribution has been collectivized. Socialism is the transitional system between capitalism and communism. All socialism either moves towards communism, or falls backwards.
As for "Stalinism," that doesn't exist. Marxism-Leninism is an ideology, the one guiding Cuba, the PRC, former USSR, Vietnam, Laos, etc. Stalin's contributions to it are extremely minor, the vast majority of Marxism-Leninism comes from Marx and Lenin.
Socialism, as it has historically existed, is by no means "fascism." Equating the Soviets with the Nazis is a form of Holocaust trivialization. The communists represent the working classes, and always fight in their favor. The Nazis created an ideology based on racial supremacy, and cemented bourgeois rule with an iron fist. They are not at all equivalent, and to do so is immensely anti-socialist.