Lewis structure

The Lewis structures, also called Lewis-dot diagrams or electron dot diagrams or Lewis dot structure are pictures that show the bonding between a pair of electrons and the atoms of a molecule.
Each dot represents one electron. Two dots side by side represent a lone pair of electrons.
To show a bond between atoms, a line representing a pair of shared electrons is placed between the two atoms. This is showing water also known as H2O.
One idea for how to understand Lewis structures.
1. First we have to select central atom.
2. Central atom is that which is present in list in number.
 if not 
3. central atom is that which has more number of valence electron.
4. Hydrogen is never central atom.
5. Then we arrange the rest of the atom and their electron as such they become stable.