Organic molecules are things like carbohydrates, fats, protein and nucleic acids (DNA & RNA).

Organic molecules are made up mainly of carbon (C), hydrogen (H) and oxygen (O).  Carbon  forms the "backbone" of the molecule.

Take a look at the carbohydrate glucose, and count the number of carbons making up the "backbone" of the sugar.

For centuries scientists assumed that these organic molecules could only arise from living cells.  That assumption begged the question, where did the first organic molecule come from? i.e. where did the first cell come from; where did life come from?  The mechanism of the origin of life is discussed in Ch. 4.