How do amino acids molecules differ from fatty acid molecules

Short Answer is: fatty acids lack Nitrogen atoms.
Amino acids are the building blocks of proteins. They are made up of the elements carbon, hydrogen, oxygen and nitrogen. They have the functional groups carboxyl (COOH) and amine (H2N).
Fatty acids or LIPIDS - [fats from animals, oils from plants] - are the building blocks of triglycerides. They are made of of carbon, hydrogen, oxygen and DO NOT contain nitrogen. They have the functional groups carbonyl (HCO) and carboxyl (COOH).