The cabin is basically a message board for people to support each other. It's similar to the groups on here. Whether you want to share what you've written is up to you.

The Camp NaNoWriMo FAQs page:
Camp NaNoWriMo

There's a lot of overlap, but if you're curious, here's a link to the FAQ's of the original NaNoWriMo:
nanowrimo.org/faq