Visualized here is  a chemical reaction, the burning of a molecule of methane.   These  are made with an organic chemistry model kit,  wherein the elements carbon, oxygen, and hydrogen are represented by the black spheres,  red spheres,  and white spheres, respectively.

 One methane molecule,  CH4, which is an atom of carbon bonded with four atoms on hydrogen, reacts with two molecules of oxygen (O2),  each of which consists of two atoms of oxygen bonded together,

rearranges the atoms to yield one molecule of carbon dioxide (CO2), and two molecules of water (H2O).

People (scientists of different types, e.g. chemists, physicists, climatologists) study interactions of these molecules in the atmosphere.   Methane, carbon dioxide, and water are all greenhouse gases in order of decreasing strength per molecule.