Socialism: A republic or a democracy can adopt some socialist principles and Socialism can co-exist within Capitalism.
Communism: A "workers'
owned nation" -- a dictatorship with equal wages for all except the Politburo and the Commissars -- they get to sponge off of and steal the wealth created by the workers. Communism creates a situation of massive wealth redistribution ( to the Communist State ) then stagnation will set in until some capitalist incentives are reintroduced. There is no real incentive to produce -- the harder you work no longer matters: You will get the same wages as a menial laborer unless you have some Communist Party status.