Elaborating upon the other response, you can break down the economy into 3 sectors (typical in Marxist economics) by what they produce
- Means of production
- Consumer goods
- Surplus goods (things consumed by the state and capitalists, like weapons, luxury items, etc.)
In a capitalist economy, the first sector is funded by capitalist exploitation and state subsidies/orders (which in turn come from taxes). The second sector is funded by worker wages and welfare (again, ultimately from taxes). The third is funded by exploitation and taxes.
The size of each industry is determined by its funding, so the state can indirectly control the size of each sector of its economy. The more it taxes workers, the smaller sector 2 becomes, leaving room to grow sector 1 and 3. Placing orders on firms to build out infrastructure or do research can expand sector 1 and so on.
Controlling the size of the sectors is the primary goal of any (rational) state's economic policy. If the state wants to grow the economy quickly, it directs funding into sector 1. If it wants to raise the standard of living, it directs it into sector 2. If it wants to prepare for war, or give its bourgeois class more private jets, it directs funding into sector 3.
This economic structure exists even in socialist societies. They may produce negligible "luxury items", but they still have to produce weapons. The difference in a fully realized socialist society is that taxes become obsolete. The socialist state can directly control the size of each sector, while the capitalist one has to use indirect means like taxes, subsidies, interest rates and so on.