If you aren't familiar with the concept, a mailing list provides one address to which you and your students send mail to have it distributed automatically to the rest. Web archives allow students to see past messages and give you an archival record of participation. Forums are web-based bulletin boards. You control who can access the forums and forum topics. No extra mail in your email inbox, and a nice way to have class discussions outside of the classroom.
Messages can have attachments of documents, images, and any other computer file.