Think of $CO_2$ like a glass roof on a greenhouse; it lets the sunlight (visible light) enter, but prevents the heat (infrared energy) from escaping, keeping the interior warmer than the outside air.

CHM (Carbon, Heat, Methane) - Remember that Carbon dioxide is the 'Champion' of heat trapping.

Greenhouse gases contain molecules that are vibrationally active in the infrared range. When solar radiation warms the Earth, the surface emits long-wave infrared radiation. $CO_2$ molecules absorb this radiation through vibrational transitions and re-emit it in all directions, including back toward the Earth's surface, a process known as the greenhouse effect.

In competitive exams, remember that greenhouse gases must be polyatomic molecules like $CO_2$, $CH_4$, or $N_2O$ to absorb infrared radiation; monoatomic gases like Helium or homonuclear diatoms like $N_2$ cannot.