What do I need before I start?

Four things, and you probably have all of them.

1. A Mac or a Windows computer to run the desktop app.
2. Google Chrome, which runs the extension that does the posting.
3. A Facebook account that you already use. The app posts through your own signed in Facebook session in Chrome.
4. Your brokerage name and, for any listing that is not your brokerage's, the permission you have to market it.

Install the desktop app first, then the Chrome extension, then sign in to the app with the email you signed up with. The full first post walkthrough is in the Help Center under "How do I post my first listing?"

Stuck on the Mac install message? That one has its own answer in the Help Center.