First, for simple changes to the website, such as fixing typos, the easiest way is to scroll to the bottom of the page, follow the link at the bottom to send a pull request, edit the resulting page, and issue a pull request.
For more elaborate changes, including adding new pages, you will need to clone the GitHub repository. You can then set up your local clone to provide a local copy of the website at http://localhost:8000 by following the instructions in the README file. This way, you can test your changes before issuing a pull request.
The handbook is the most updated part of the website and it includes quite a bit of infrastructure to support writing pages that describe features in any or all of the target languages. The root of the handbook pages in the
packages/documentation part of the repo. That directory has a useful README file that describes the structure and provides instructions for inserting code examples in any target language and target-specific text within a body of target-independent text.