Conference proceedings may be lighter publishing than Journal papers.
Conferences are also interesting for tutorials and workshops that people go to learn.
Papers are still peer-reviewed. They are sent to at least one or more reviewers.
Peer-review full content is only open to the Conference Committee staff. Excerpts of reviews are shared with submitting author (nominated person if >1 author) regardless of whether paper is accepted or not, as feedback can help improve later submissions by rejected authors.
A committee organizes a Conference and is responsible for the peer review process by selecting a group of voluntary reviewers.