what exactly is the greenhouse effect?

Reference from www.climatechangeandyou.com

What is GHE (Green House Effect)GHE is a way of describing what happens in a greenhouse, covered in glass.

The glass is transparent to sunlight, so the light waves cross the glass, and reach the objects inside, ie plants, soil, pots, etc…When any of these bodies is touched by light, it reflects some of it, and absorbs some of it.The absorbed light is converted to heat, and the body warms up.As the body warms up, it radiates more energy in the infrared.And now to the important fact that ties it all together : Glass in not transparent to infrared radiation. So, when the plants, pots, and soil in the greenhouse radiate in the infrared, this wavelength cannot exit back out of the greenhouse. The glass reflects it back inside. So the energy is trapped in the greenhouse, and it warms up until the energy balance is re-established. Therefore, a glass greenhouse is an energy trap.

Why is it importantThe GHE is essential for the survival of animals and plants on Earth.
Without GHE the Earth would be too cold, and become an ice planet.With too much GHE the Earth will warm up even more, causing catastrophic changes to the weather, the oceans, forests, etc…Life on Earth exists on a fine balance of GHE, that is, a fine balance of energy input and output.
The main energy input is the amount of light that the earth absorbs from the sun, ie the energy that enters the atmosphere, minus the energy that is reflected back out to space. Another energy input, is the considerable amount of energy that is released by human activity on earth by burning fuels, mainly for transport and electricity.

The end result of most energy use is the release of heat to the air or to the water.The energy output, is the amount of infrared radiation that the earth looses to space.Some gases in the earth’s atmosphere behave like the glass in a greenhouse. They are not transparent to the infrared radiation, and reflect the infrared back to the earth.These are called the GH gases, and their amount in the atmosphere is of extreme importance to the climate regulation on Earth. More on this later.
you should google it for yourself and watch the David Attenborough video below.
Learn as much as you can!