Picture this. You are standing on Earth. Suddenly, the Sun disappears. This would cause all living things on Earth to die.
The Sun is a star. It is not the biggest or brightest star. But it is important to us. How? If the Sun wasn't here, you would not be reading this. I wouldn't even be able to write this. The Sun gives us light. The light lets us grow plants and animals. Then we can use the plants and animals for food. On Earth, we can only see the Sun in the morning. Why? At night, we cannot see the Sun. We are facing away from the Sun.
The sun is in a galaxy. That galaxy is called the Milky Way. In one of the spiral arms, there is the Solar System. In the center of the Solar System, is our Sun. In the core of the Sun, it makes lots of energy. Later, the energy exits the core. When it reaches the surface, it is shot out at the planets. When the light hits the planet's surface. On Earth, a carbon dioxide layer traps most of the light. Some escapes into space.
You get the point. The Sun is a life-giving star. But sometimes our Moon blocks the Sun. This is a solar eclipse. There are 3 diffrent solar eclipses. They are total, annular, and partial. I don't have to explain them, so I won't. So after reading this, you should be able to awnser the question: Why do we need the Sun?
If Sol suddenly disappeared, it would take about 8 minutes for us to notice, due to the time is takes light and gravity to propagate toward Earth.
Water vapor actually traps more of Sol's energy than carbon dioxide, just because there is so much more. I've read estimates that say Earth is 30 degrees (F) warmer than it would be without the water vapor. Aside from water, all the other greenhouse gases are fairly insignificant at the levels they have been for eons.
This blog gives a good overview for all to easily understand without getting into the scientific details that can cause spontaneous cranial explosions.