Click the "+" icon and add three C (carbon) atoms. Place the central carbon atom (CO) between the two outer carbon atoms (CH₃). Notice that the central carbon has four unpaired electrons, while the outer carbons each have three.
Click the "+" icon to add one O (oxygen) atom. Oxygen will have two unpaired electrons.
Click the "+" icon to add six H (hydrogen) atoms.
Click on one unpaired electron of the central carbon atom and one unpaired electron of the oxygen atom to form a single bond. Do it again.
Click on each unpaired electron of the outer carbon atoms, then click on an unpaired electron of a hydrogen atom to form single bonds. Repeat until all hydrogen atoms are bonded.