Yes, fleas are parasites that obtain food by eating the blood of their hosts, which can be any warm-blooded vertebrate animal. We normally associate flea bites with dogs and cats and other pets, but fleas can also bite humans as well.
Not only do fleas eat blood, but a blood meal is required for a flea to progress from the larva or pupa stage of the lifecycle into an adult flea. If it cannot obtain a blood meal within one to two weeks, it will quickly die.
Adult fleas need to eat blood in order to reproduce, and after an adult female flea has obtained blood it will quickly lay approximately 20 eggs, usually directly on the hair of its host.
The flea has a long tube like appendage coming from its mouth, which functions as a sort of tiny hypodermic needle used to extract and eat the blood of the host.