Kingdom is the broadest division.
The lowest, most basic division is species, which consists of organisms that resemble each other and are capable of interbreeding to produce fertile offspring. The first name is the genus, the second is the species. For example, a lion is Panthera leo, a tiger is Panthera tigris. The first word is always capitalized, the second is not, and both should be italicized. Humans, of course, are Homo sapiens.