Coinbase is a platform or is a service for digital currency. Through coinbase, you can buy, sell, transfer and store your digital currency on coinbase. The features coinbase has include,
You can buy and sell the digital currency(cryptocurrency)
You can have a wallet on coinbase
You can send and receive cryptocurrency from online wallets, friends, merchants FOR FREE.
Security, backups are taken care of by them
Applications are being built using their API. API is a set of functions and procedures that allow the creation of applications which access the features or data of an operating system, application, or other service.