To develop a deeper understanding of what ontologies are, how they work and how they are created, the following guide is an excellent place to start.

Using ‘wine’ as a case study, it takes the reader through the steps (and approaches) associated with creating an ontology. As well as reading the guide, it is recommended to follow along with the exercises in order to develop a deeper understanding and first hand knowledge of ontology creation:

http://protege.stanford.edu/publications/ontology_development/ontology101-noy-mcguinness.html