What is/are the difference(s) between socialism and communism?As far as I understand it, socialism is a branch of communism. But where do the...

Follow the link below for a discussion of the differences
between socialism and communism from a Marxist
perspective.

I would not say socialism is a branch of
communism, at least not in Marxist thought.  To Marxists, socialism is a step that has
to come between capitalism and communism.  Under socialism, a country can keep a
democratic form of government, for example, and just have it be run by socialists rather
than by capitalists.  They would just use the existing
system.

Under communism, the whole system that was in use
under capitalism is blown up and something completely new is put in
place.

It is hard to talk about these in terms of the
Soviet Union because it did not really replace a capitalist system.  The Soviets called
themselves socialist, though, because they needed to have a big system of government. 
They supposedly believed that they would not need that government after true communism
was achieved.