Messages is your in-app inbox: it's the only way conversations happen between members. Nobody's real email address is ever shown or used.
How a conversation starts
You can't start a brand-new conversation from the Messages page itself: there's no "compose" button there. Conversations begin on the Marketplace, when you click "Contact seller" on a listing and send a first message. After that, it lives in your Messages inbox and either person can reply from there.
Using your inbox
The inbox lists every conversation you're part of, newest first, with the other person's name, a preview of their last message, and an unread indicator if there's something new. Click a conversation to open and reply: opening it marks it as read automatically.
A small unread badge sits on the message icon in the navigation bar on every page, so you won't miss a new message no matter where you are on the site.
Related articles: Marketplace