IT IS WARMER IN THE SUMMER BECAUSE THE EARTH IS CLOSER TO THE SUN
WRONG!!
A common misconception (thanks to TOM)..
Although the distance of Earth/Sun varies a little is is not responsible for hot summer and cold winter...well..it CAN'T be because it is winter in the Southern Hemisphere when it is summer in the Northern.
The Earth is tilted on its axis. In the Northern Hemisphere in SUMMER the tilt is towards the Sun. This means that the rays are coming from more overhead (you can see that by the position of the Sun in the sky). This means that the Power arriving from the Sun is "more concentrated" (technical: the Intensity or power per square metre is greater). If the power is more concentrated it means that the Earth at that point will heat to a higher temperature. In the winter Northern Hemisphere the tilt is away from the Sun so the Intensity is less....the power is less concentrated. You can get an idea of this by shining a torch at right angles to a piece of paper and looking at the circle of light - now tilt the paper and you will see that the light is spreading over a bigger area so it is less concentrated.
I have seen pictures showing that on the side tilted towards the Sun it is hotter than the side away from the Sun by showing it as towards the Sun on one side and 6 months later on the far side from the Sun...but think about it....the Earth is rotating on its axis every day and the side towards the Sun is simply daytime and the side away from the Sun in night time.
Apologies to readers in the Southern Hemisphere...I have nothing against you but I am in the Northern!!!...just reverse all the ideas above!!!