The axis of the earth is tilted at approximately 23.4° with respect to the orbital plane of Earth. The tilt of the axis of the Earth is the reason for seasons on Earth. At any point in time, one of the latitudinal hemispheres will be closer to the sun as compared to the other hemisphere. Thus, that hemisphere will be heated more and will experience summer season and the other will experience winter season. If this tilt was not present, each half of the earth would be equally heated and ocean currents would slow down considerably.
Also, since the earth is spherical, the poles are heated less that the equators. Sun rays fall obliquely on the poles and hence heat the area to a lesser extent and compared to the equatorial region, which recieves the sun rays almost perpendicularly. This also causes wind and ocean currents, which are important in distributing the heat throughout the planet.
The images give a visual understanding of the concept (images not to scale).