Why should I use address book?
Ethereum's address and Bitcoin's address are both strings of hash. Because of the long string of randomized combinations of letters and numbers, it is easy to transfer to a wrong address. There are two ways to solve this problem: ENS domain and address book. However, the current penetration of ENS domain names is low, so the address book is a better choice.
How do I add an address?
How do I use address book when transferring?