Notes are the fundamental data structure in Aztec when working with private state. In this section there are guides about how to work with AddressNote, ValueNote, and custom notes in Aztec.nr. You can learn more about notes in the concepts section.
Address notes hold one main property of the type AztecAddress. It also holds npkmhash and randomness, similar to other note types.
It may be useful to write a custom note type if you want to use a specific type of private data or struct that does not have a default implementation in Aztec.nr. If you create a note that uses a custom note type, you are able to nullify that note with one nullifier. This is more secure and less expensive than using multiple separate notes.
ValueNotes hold one main property - a value - and have utils useful for manipulating this value, such as incrementing and decrementing it similarly to an integer.
Core knowledge of Notes and how they work