A Molecule is basically an electrically neutral group that is made up of at least two atoms in a definite arrangement. Molecules are characterized by a chemical bonding between the atoms.
A molecule usually consists of atoms of same chemical element or of different elements. Such as Oxygen molecule has two oxygen atoms whereas water has two hydrogen atoms and one oxygen atom.
Various types of bonding is used to join the atoms in a molecule. Mostly, they use covalent bonding. Apart from that hydrogen bonding or ionic bonding is also used.