Well, Karl Marx was a communist, so he writes about communism and how socialism is just the means to Communism, which you would know if you actually read his work. He says in "Critique of the Gotha Programme" published in 1875 - “Between capitalist and communist society there lies the period of the revolutionary transformation of the one into the other. Corresponding to this is also a political transition period in which the state can be nothing but the revolutionary dictatorship of the proletariat.” IE - Socialism is just a transitional stage to communism, but already beyond free market capitalism.
From "The Communist Manifesto" published in 1848: “The theory of the Communists may be summed up in the single sentence: Abolition of private property.” Granted this doesn't mean all property, but private ownership of productive assets like factories, land, and capital. In other words: do you own a business? Now you don't. Do you own some land? Now you don't. Do you own the ability to make goods to sell to others? Now you don't; the state owns it now.