I assume that you are asking about the economic policy that was promoted by people like Henry Clay and, before him, Alexander Hamilton. This was a policy that was meant to create the sort of national economy based in part on manufacturing that these leaders preferred to have. There were three main aspects of the American System. These were a tariff, a national bank, and federal subsidies for “internal improvements.”
Let us look at each of these in turn. A tariff was something that leaders wanted because they felt it would promote American manufacturing. It would increase the prices of imported goods, making it easier for domestic goods to sell. The national bank was meant to create a stable currency. It would issue money that would not lose its value. This would make business more predictable in the US. Finally, “internal improvements” were meant to improve the ability of people to trade within the US. These improvements were to the country’s transportation system. The point was to make things like better roads to promote the movement of goods from place to place.
With these three components, Clay and others like him hoped to create a stronger national economy.