Basic rules
Big picture​
Use Calico policy rules and label selectors that match Calico endpoints (pods, OpenStack VMs, and host interfaces) to define network connectivity.
Value​
Using label selectors to identify the endpoints (pods, OpenStack VMs, host interfaces) that a policy applies to, or that should be selected by policy rules, means you can define policy without knowing the IP addresses of the endpoints. This is ideal for handling dynamic workloads with ephemeral IPs (such as Kubernetes pods).
How to​
Read Get started with Calico policy and Kubernetes policy, which cover all the basics of using label selectors in policies to select endpoints the policies apply to, or in policy rules.