Hello!
An atom is the basic unit of life. It is made up of protons, neutrons, and electrons, and it they up everything, including molecules. An atom is an element based off of how many protons it has. One example of an atom would be an oxygen atom.
These elements (atoms) make up molecules. When atoms are bonded together, they form a molecule. One example of a molecule would be H20, where the 3 atoms are bound by covalent bonds.
Hope this helps!