The picture below will help you ‘get to know’ your pet budgie, showing the basic external anatomy and helping you tell your vent from your cere.
The majority of the body parts labelled here are common to all bird species. The features that make this very clearly a budgerigar rather than any other type of bird are the cheek patch and throat spots. Not all varieties of pet budgies have these, due to the complexities of the bird's colourful gene pool; but all wild budgies have them, and they are an important part of the bird's body language. Budgies' keen vision is able to pick up the ultraviolet light reflected from the cheek patches. They might just look like blue or green splodges to us, but they are as striking as a firework display to a budgie's sensitive eyes.