defining user roles to restrict read & write permissions

I’m considering using WP for a (small) community site (<30 users),
where users should have different capabilities depending on their
roles. In particular, I’d like to have parts of the site readable
only to a subgroup of users (some committees using their own
forum within the site, say).
Is that already possible ?

Capabilities that I have found so far all revolved around writing /
posting, or changing settings, but not reading. Also, I didn’t find
mention of custom roles to which I could assign page-specific capabilities.

Any help is highly appreciated !