It consists of many steps and each step is mentioned as a rank or category. Each category is a unit of classification. Various levels in taxonomic hierarchy are:
Species —> Genus —> Family —> Order —> Class —» Phylum —> Kingdom.
(a) Similar individuals form a group called species. All the related species form the next rank genus, e.g., Rana tigrina (Frog), Ram is genus and tigrina is species.
(b) Related genera are kept in a family e.g., Petunia, Solanum and Datura are the members of family Solanaceae. The related families comprises Order e.g., Solanaceae and Convulaceae comes in order Polynomials.
(c) All orders make classes, e.g., bony fishes and cartilaginous fishes are included in class Pisces.
(d) Various classes like amphibia, aves, mamamalia form a Phylum (Chordata), and all Phylum comes in kingdom Animalia.