What is the secret key in Coinbase?

Could you please elaborate on what exactly the secret key is in the context of Coinbase? Is it a unique code or password that grants access to one's account and funds? Is it something that should be kept private and secure at all times? Additionally, how does one manage and protect their secret key to ensure the safety of their cryptocurrency holdings on Coinbase? It would be helpful to understand the importance of this key and the steps that users should take to safeguard it.