We can always use help answering questions at Let’s Encrypt Community Support. See this blog post about why community support contributions are so important.
We can also use help with software development. All of our code is on GitHub.
Certbot is a Python-based utility that works alongside your webserver to automatically obtain a certificate and convert a website to HTTPS. Certbot is the client we recommend that most people start with. Many other third party client options are available.
Boulder is the Let’s Encrypt CA implementation. It’s based on the ACME protocol, and written primarily in Go. A great place to start is with the list of ‘help wanted’ issues and the contributors guide.
You can improve this website and the documentation here or help with its translations.