There are lots of ways to contribute to Kubernetes. You can work on designs for new features, you can document the code we already have, you can write for our blogs. There's more: you can implement those new features or fix bugs. You can help people join our contributor community, or support existing contributors.
With all these different ways to make a difference to the project, we - Kubernetes - have made a dedicated website: https://k8s.dev/. You can go there to learn more about contributing to Kubernetes.
If you specifically want to learn about contributing to the documentation or other parts of this website, read Contribute to Kubernetes documentation. If you specifically want to help with the official Kubernetes blogs, read Contributing to Kubernetes blogs.
You can also read the CNCF page about contributing to Kubernetes.