This area of chemistry is all about one element; carbon. Organic molecules are built around a central carbon atom (or atoms) and have thousands of uses in everyday life. The starting point when learning about this area of chemistry is to look at what all organic molecules are based on- hydrocarbons.
What is a hydrocarbon?
This is a really simple definition, so learn it! "A hydrocarbon is a compound containing carbon and hydrogen only". This is normally worth 2 marks in an exam!
Because carbon is in group 4 of the periodic table we know that it has 4 electrons in its outer shell. That means that it is looking to complete its outer shell by either sharing 4 electrons, or gaining/losing 4 electrons. Because carbon is a non-metal it will always look to share electrons, so it will always look to form 4 covalent bonds. Let's look at the simplest hydrocarbon for an example:
See how the carbon atom is joined to 4 hydrogen atoms, to complete its outer shell of electrons.