Each node runs services to run containers and be managed from the master.
In addition to Docker, Kubelet is another key service installed there. It reads container manifests as YAML files that describes a pod.
Kubelet ensures that the containers defined in the pods are started and continue running.
To learn more about Kubernetes and familiarise with its terminology along with a bit of hands on do refer to:
https://www.edureka.co/blog/kubernetes-tutorial/