Secrets is an object in Kubernetes which is used to store sensitive information, such as username, passwords, etc., with encryption. This is a much safer way to store information, rather than piling up in a Pod, and container image in Kubernetes.
If you wish to learn Kubernetes and get certified, then check out the Kubernetes certification course from Intellipaat. And if you want to know more about Kubernetes, watch the following YouTube video on Fleet Management for Kubernetes.