The income statement covers a span of time, usually a quarter or a year, unlike the balance-sheet, which is a snapshot of one day. It starts with revenue, subtracts cost-of-goods-sold to get gross-profit, subtracts operating-expenses to get operating-income, then subtracts interest-expense and income-tax-expense to arrive at net-income.
It is built on accruals, not cash. Revenue is booked when the sale is earned, not when the customer pays, which is why the cash-flow-statement often tells a different story in the same quarter.
Example: Northwind Tools reports revenue of $840M, COGS of $470M, operating expenses of $250M, interest of $18M and tax of $24M. Gross profit is $370M, operating income is $120M, and net income is $78M.
Related: revenue, net-income, operating-income