Wind is mainly the outcome of a thermodynamic principle and
of the coriolis effect due to the rotation of the earth towards
the east (counterclockwise). Warm air
around the equator is lifted, which creates a suction effect for air
masses coming from higher (or lower) latitudes. The high altitude air
masse move either north or south until their temperature is low enough
for them to "sink" and start to converge towards the equator.
As these air masses move, the coriolis effect shift their
direction. The outcome
is a system of circulation known as a "cell"; three of which are between
the equator and the North Pole (and vice versa for the South Pole).
The most significant is the Hadley Cell from which the "Trade Winds"
are the outcome.