It's a good idea to learn the names of the different parts of a bird's anatomy - that way, you'll know what the books and websites are talking about when they use words like cere, crown, and wing coverts! The illustration below reveals all.
Note: Most of the things labelled in this picture apply to all bird species. The features that make pet parakeets distinctive are the cheek patch and throat spots. In the wild, all parakeets have these, but in captivity some breeds have almost lost these features. The birds have very good eyesight, and they are able to see ultraviolet light reflected from the cheek patches. To us they may look like blue or green splodges, but to a parakeet these flashes of ultraviolet are as striking as a 4th of July firework display!