All the energy our planet receives from the Sun. As our Earth was round, that the sun's rays fall on the surface at different angles. So at the equator and in the tropics, where they reach Earth via the most direct route, just hotter. As it moves poleward heat decreases, because the sun's rays have to travel through the atmosphere to a better path, and, besides, to irradiate a large area. Therefore, the air here receives less heat.
If all the earth's atmosphere is heated evenly, the air is rising up, getting warm, and down, cooling down. But at the equator is significantly warmer than the polar zones. In the tropics, the warm air rises and rushes to the poles. Already near the thirtieth latitudes of this air, cooling down, goes down and is re-directed to the equator, where the pressure is lower. The so-formed constant winds the trade winds, which in the Northern hemisphere blow to the North - East and South - South - East. The name of the wind specifies the direction from which he came.
The other part of the Equatorial air continues at the top of his journey to the poles. So there are westerly winds. Over the poles cold air descends and is re-directed to the tropics. On the equator usually reigns calm.
The wind direction is also affected by the Earth's rotation from West to East. So the winds of the polar zones on the way to the equator are deflected in the Northern hemisphere to the right, and in the South to the left.