Mailing lists are just like Yahoo groups/Google groups. You subscribe to a mailing list and become a member of that. Each mailing list will have it's own set of mailing rules just like each forum has it's own set of posting rules.
One thing that can seem difficult with mailing lists is how to keep track of a particular discussion. In forums you have a
thread for a discussion. Whereas for mailing lists, each reply to a discussion is a separate mail. Fortunately most mail clients have an option to group messages by subject line. In web based mail clients, Gmail has that facility. That's why most mailing lists actively discourage you to change subject line while replying to a mail.
