What’s the best way to learn and build my first Kubernetes CRD?

A good progression is to build a tiny controller from scratch first, then recreate it with controller-runtime. Once the concepts make sense, move to Kubebuilder or Operator SDK. Go is the most common choice for this ecosystem, so learning basic Go alongside the Kubernetes API will probably pay off, even if you initially prototype ideas in Python.

Start with the official Kubernetes documentation on CustomResourceDefinitions so you understand the API structure, schemas, validation, versions, and how custom resources are created and queried. Begin with a very small resource containing only a couple of fields, apply it to a cluster, and inspect what Kubernetes stores and returns.

Choose a small practical project where the custom resource describes desired state and a controller makes the cluster match it. For example, you could create a resource that manages a simple application configuration or deployment. After that, try a more advanced project such as coordinating groups of workloads, but avoid starting with a scheduler because it introduces several difficult Kubernetes concepts at once.