The best place to find information and resources to be able to participate and support SIG Architecture's work is to visit the Architecture Special Interest Group Github repo and the README file. You can also learn more about the SIG Architecture Charter following the link.
Joining the mailing list will get you invited to our meetings.
Our Regular SIG Meeting is Thursdays at 11:00 PT (Pacific Time) (biweekly). This would be a good place to start.
There are also various Working groups and Subprojects meetings where new contributors are always welcome.
Contributions are made via Pull requests. Before opening a pull request, contributors must sign the CNCF Contributor License Agreement
Feel free to ask any questions in the #sig-architecture Slack channel through the Kubernetes Slack. To get a Slack invite, visit http://slack.k8s.io/ . Once you're logged you can join the channel. Alternatively, you could join any one of our meetings.