It isn't unusual for a person to wonder why the north and south poles are cold, while the equator is so hot. To understand the reason for this, it is helpful to know a little bit about the earth and a little bit about the solar system.
The earth revolves around the sun about once every 365 and a quarter days. The orbit isn't a circle, however. Instead, the orbit is an ellipse. This means that at some times of the year, the earth is several million miles closer to the sun than it is at other times of the year. This is important because most of the earth's heat comes from the sun. It should be noted, though, that the distance from the sun doesn't have a huge impact on the seasons or temperatures.
As the earth revolves around the sun, it doesn't do so at a perfectly perpendicular fashion. The planet actually tilts by a bit more than 23 degrees. This means that at one point during the year, the northern hemisphere is tilted toward the sun and the southern hemisphere is tilted away from it, while about six months later, this is reversed. Interestingly, the winter in the northern hemisphere corresponds to a time when the earth is closest to the sun but is tilted away from it.
The angle of tilt means that even in the height of summer, sunlight is coming in at an angle. Because of this, the light must go through more of the atmosphere before it reaches the surface. It doesn't heat as efficiently, since the sunlight is weaker, so the poles are colder than they would be if the sun was directly overhead. Precipitation usually falls as snow, and the cold means that it doesn't readily melt. In fact, much of Antarctica is technically desert, but the snow doesn't melt because of the temperatures.
Reflective qualities of snow and ice
The earth's orbit and angle explain why snow falls at the north and south poles and why it is cold, but it isn't the whole picture. Snow and ice also reflect sunlight. This is called albedo, and it means that the sunlight doesn't have the chance to warm the air enough to melt the snow and ice. Instead of melting, the ice builds up, further reflecting the heat-giving sunlight away.
The oceans are very efficient at transferring and transporting temperatures. The currents are also responsible for generating enough moisture for the snow to fall on both poles. Currently, there are few land masses in the way of the ocean currents, so the poles are warmer than they've been in the past. In the past, when the currents have been blocked by land masses, the poles have been even colder than they are now.
The result of the orbit, angle, albedo and ocean currents is that the poles are incredibly cold. Places in Antarctica are constantly below the freezing point of water. There are also places there where the ice is over a mile thick.
The north and south poles are always cold today, though at times in Earth's past, there has been no ice caps. There are more factors involved in keeping the poles cold than only those mentioned here, however it is likely that the poles will remain that way until there is a substantial change in the causes that have been mentioned.