To use ConfigMap inside a pod, you'll have to use configMapKeyRef as the value source in the env section. This will populate whole ConfigMap pairs to environment variables:

# cat 3-2-3_pod_ev_configmap.yaml
apiVersion: v1
kind: Pod
metadata:
  name: configmap-ev
spec:
  containers:
    - name: configmap
      image: centos
      command: ["/bin/sh", "-c", "while : ;do echo $DATABASE_ENDPOINT; sleep 10; done"]
      env:
        - name: DATABASE_ENDPOINT
          valueFrom:
            configMapKeyRef:
              name: example
              key: database.properties
// create configmap
# kubectl create -f 3-2-3_pod_ev_configmap.yaml
pod/configmap-ev created
// check out the logs
# kubectl logs configmap-ev
endpoint=k8s.us-east-1.rds.amazonaws.com port=1521

The Kubernetes system itself also uses ConfigMap to do some authentication. Check out the system ConfigMap by adding --namespace=kube-system in the kubectl describe configmap command.