Molecules are the general term used to describe atoms connected by a chemical bond.
So all combinations of atoms are molecules.
Next lesson: States of matter
Compounds are molecules made up of atoms from all sorts of different elements.
So all compounds are actually molecules, but beware, not every molecule is a compound.
For example, Hydrogen gas (formula: H2) is actually a molecule. However, it is not a compound as H2 is made up of just one element.
Water (H2O), on the other hand, may be called both a molecule and a compound as it is made up of oxygen (O) and hydrogen (H) atoms.
You can write every molecule as a list of all the atoms that form them.
For example, we write NaCl as the way to represent table salt (the molecular formula) that formed through an ionic bond between chlorine (Cl) and sodium (Na).
A molecular formula may also be used for a covalent molecule like water (H2O).
In case we see more than just one atom of any particular element within one single molecule, we are using a subscript number at the right side of the symbol for the atom to indicate the number of atoms of that specific element present in every molecule.