How can a build-up of carbon dioxide in the atmosphere increase Earth's global temperature?

Due to carbon dioxide sunlight get trapped in earth's atmosphere, increases the temperature and results in global warming. Due to this glaciers melt and sea level increases and hence coastal areas may flood. The sun's rays reach us in the form of visible light, and raise the temperature of earth. This heat energy warms the earth then goes back into space, and so the temperature remains in balance.