Yesod has an active, vibrant community that is happy to help you get started. If you want to get involved, you should check out:

Stack Overflow for help questions. Make sure to include the Yesod and haskell tags.
Yesod google group for Yesod specific discussions. There is also a very low traffic web-devel mailing list for more general haskell web development discussions.
IRC channel Freenode#yesod For help, brainstorming, or just hanging out. Activity varies greatly - don't expect your burning issues to be answered or even anyone to be available to respond - please use StackOverflow and the google group if you must get feedback.
Github Issue Tracker for reporting bugs. If you are unsure if you are encountering a bug, ask on the mail list or on IRC. If you have an installation error, please report on the mail list.
Yesod Wiki This is a great place to post documentation and tutorials.
Haskell Reddit is a good place to share Yesod related blog posts.

If you want to participate with Yesod even more, we have two highly recommended approaches for beginners:

If you want to dig into the codebase itself, please check out the Yesod issue tracker and pick something to work on. If you have any questions, the mailing list are IRC are great places to get some help.