The earth is tilted 23+ degrees from what the layman might describe as straight up and down. Most all globes illustrate this by angling the poles of the globe by 23+ degrees.
The earth orbits around the sun in a slightly oval orbit, at a distance of about 93,000,000 (93 million) miles. I say about, because in January, it reaches its closest point (perihelion) and in July it reaches it furthest distance. (aphelion). The differences between the closest point and the furthest point is not very great, so we generally think of the orbit as being 93 million miles plus or minus a few million miles or so. For more detailed explanation click on: http://www.museum.state.il.us/exhibits/ice_ages/why_glaciations1.html#eccentricity
The tilt is responsible for our seasons. In the Northern hemisphere, (Everything north of the equator) we experience winter in December and January. We experience winter because the tilt of the earth faces the Northern hemisphere away from the Sun. While facing away, we get shorter periods of sunlight, and the Sun is striking the Northern hemisphere at a shallower angle, so less heat energy is being absorbed by the parts of the earth in the Northern hemisphere. At the same time, the Southern hemisphere is tilted toward the Sun, receives more Sunshine each day, and the Sun is more direct, thus heating the earth more strongly, so they experience summer. During June and July, the tilt works the other way. The Northern hemisphere is tilted toward the Sun, and we experience summer. Again, this is because the Sun is beating down more directly on the Northern hemisphere, and there are more hours of daylight each day because of the tilt.
During the Spring and Fall equinoxes, (March 21 and Sept. 20) the tilt of the Northern Hemisphere is midway between being toward the Sun or away from the Sun. Each hemisphere receives equal daily amounts of Sunshine, and the Sun is seen as being over the equator, giving each hemisphere the same duration of daylight.
If we were able to change the tilt, very interesting things may be possible. We could moderate the extremes of Winter and Summer. If we slowly, carefully, over many many years, reduced the tilt toward zero, it's possible we could achieve balanced and moderate weather over the entire earth. For further on this topic, See Control Weather Extremes.