There are two sides to any transaction. There is a seller, and there is a buyer. To use an example, when you enter a store to purchase something, you are the buyer. The store, or its owner, is the seller. For instance, if you purchase a soft drink for $2.00, you have expended—or spent—$2.00, and in exchange, you have received a soft drink to consume.
Aggregate expenditure measures the aggregate spending activities of the overall economy. Aggregate expenditure, or Gross Domestic Product (GDP), consists of household consumption, which is denoted by “C,” plus investments, denoted by “I,” plus government spending (“G”), plus net exports (“NX”).
Aggregate expenditure = C + I + G + NX.
It calculates the total value of economic activities within the country's economy and is also called gross domestic product (GDP).
Household consumption is the amount that people or the general population spends. In the example above where you purchased a soft drink, you contributed to household consumption.
Investment is the amount that the economy saves. If, for example, you earn $100 each week and spend $80, with the remaining $20 deposited in your savings account, you have contributed $20 to the country's I or gross investment.
G equals the amount that the government spends which is earmarked for many expenditures, including maintaining the country's infrastructure and providing law enforcement, among other activities.
Net exports (or imports) are the difference between total imports and total exports. In other words, if the country purchases $100 of goods from foreign countries and also sells $80 of internally produced products in international markets, then the net value is $20 of imported product. Conversely, if the country sells $100 in international markets and purchases $80, it is a net exporter of $20 worth of goods.