Kubernetes can use YAML files for configuration. The book Kubernetes in Action by Luksa refers to these files as manifests (pages 148), YAML manifests (page 155) or "pod manifests" (page 451). The Kubernetes website refers to this YAML file as "the PodSpec" here. Pod templates are defined inside these .yaml files (as a subset of the file itself). How do you use these YAML files?
To create one, know that there are maps and lists. Lists have merely arguments. Maps are key-value pairs. Quotes around the keys and values are optional. There should be no "tab" keys when formatting them. To learn more about the formatting, you can see this external posting.
2. You can make changes to services that already exist with these .yaml files. You would run a command like this:
kubectl apply -f filename.yaml
The resource specified in the .yaml file named "filename.yaml" will be updated accordingly.