The centrally planned economy of socialism takes the form of a 5 year plan. The plan is determined by State planning committee, Gosplan for USSR or SPK for GDR for example. The plan would be something like (make 1 million trucks, 50 million shoes, X tons of corn) and was determined by the projected needs/wants of the population and economic developmental goals. The state extracts surplus value via a turnover tax from the domestic economy and profitable exports from the international market. There were smaller taxes and fees but exports and turnover taxes made the bulk of state revenue for socialist countries. The economy produced goods and services based on human need instead of the mere profit maximization by commodity exchange under capitalism. The 5 year plans were amazing and allowed the USSR economy to grow rapidly under the Great Depression unscathed while capitalist states contracted. You can watch an excellent video on the 5 year plans in the early USSR by Finnish Bolshevik on YouTube.

Here is the link to it :  https://youtu.be/e4YDkWzQZAw