@[email protected] and @[email protected] already provided good answers to this question, so I will just add my 2 cents.
I dislike the term state capitalism, because capitalism per se is a state system. The nation-state is the way the bourgeoisie thought it would be best to organize a country ever since the end of the monarchies in Europe in the 19th century. Nation states have laws (which secure private property, and how agents that hold private property should engage each other), have clearly defined borders, an official language (in feudalism many villages within a territory would speak many different dialects), concentrate all the power of violence and bureaucracy under the nation-state (a move that started to happen since the advent of absolutist monarchies), will issue a currency and will define the laws on how foreign actors will engage in the domestic economy.
So the capitalist market is a superstructure created by the nation-state to uphold the interests of the capitalists. The state creates the conditions for the market to exist. It creates the entire legal framework that is used by the market, and even runs state services (transportation, energy generation, police, roads, railways, airports, military, diplomacy, urban zoning etc) that will support capitalist enterprises. There is a dialectical relationship between the market and the state, both a positive relationship, as the market depends on the state to exist and a contradiction in the sense as the market battles the state bureaucracy to have more power over it (as in neoliberalism) and/or the state fights the market in order to establish the dominance of state-based economic development (as it happened in the Keynesian phase of post WW2).
Note that socialism and capitalism are not different from each other because of economic planning. Both Japanese and South Korean economies heavily depended on central planning, with South Korea having a dictatorship and central planning that was even more centralized than we ever had in the post communist revolution China. The SK state was draconic with capitalists regarding their returns and how they should invest their capital and they would be disposed if they didn't achieve state development goals.
This reasoning about planning was what motivated Deng Xiaoping's market reforms in China:
Why do some people always insist that the market is capitalist and only planning is socialist? Actually they are both means of developing the productive forces. So long as they serve that purpose, we should make use of them. If they serve socialism they are socialist; if they serve capitalism they are capitalist. It is not correct to say that planning is only socialist, because there is a planning department in Japan and there is also planning in the United States. At one time we copied the Soviet model of economic development and had a planned economy. Later we said that in a socialist economy planning was primary. We should not say that any longer.
So the idea that state-capitalism is an initial form of socialism is wrong. The real question is, who holds power over who? The communist party, controlled by fractions of the proletariat is the controller of the state in the case of socialist economies. In capitalist economies, even in case of countries with good welfare programs, the state is still controlled by the bourgeoisie. Let's never forget the politics in political economy. This is essential to understand how both capitalism and socialism work. Let's not fall in the same trap the traditional neoclassical economists do in order to label economic systems.