Light and heat pour from the Sun and hit Earth more directly at its equator than at its poles. Air at the equator, therefore, gets hotter than at the poles.
Heat passes from warmer to cooler bodies.
Hot tropical air moves towards the poles in huge convection currents that force cold polar air towards the equator and cause winds. The winds drag across vast areas of sea and pull the surface water in the same direction, especially where waves increase the friction between wind and water. The Earth rotates from west to east and moves out from under the atmosphere as the warm air moves north and south towards the poles. This makes the pole-heading currents appear to curve to their right in the Northern Hemisphere and to their left in the Southern. In the Northern Hemisphere, great warm winds sweep up from the equator toward the pole, curve to their right, move into a clockwise circular pattern over the Atlantic Ocean, and bring cool polar air back to the equator.