Click the big cookie to get more cookies. Click the building tabs on the right to buy a building, provided you have enough cookies to pay for them. Buildings will produce cookies for you, and you can buy all twenty of the ones in the real Cookie Clicker. To scroll through the buildings after unlocking the Time Machine, use the up and down arrow keys. To buy buildings in bulk, hold down X while clicking to buy 10, and C while clicking to buy 100. You can also hold down S to sell a building at a quarter of its buy price, and you can hold down either X and S to sell 10 of a building, or X and C to sell 100 of a building. If you don't have 10 or 100 buildings to sell, you will simply sell all of your buildings and get the appropriate amount of cookies returned to you. Click the upgrades on the top right as you unlock them to buy them. They will increase the effectiveness of either your buildings, click power, or overall CpS. You can mouse over the building tabs and icons for further information, and you can click the "Info" button to view the changelog. You can also click "Stats" to view the achievements you've unlocked, as well as other game stats.
Credits: * Orteil (the guy who made the real Cookie Clicker) @Griffpatch-Academy @awesome-llama-test @GarboMuffin @aespibr