Simply, open your web browser of choice and visit https://horizon.auburn.edu.  

Next, select the browser option and login.

Note: When you log in, you will be prompted to verify your identity via the DUO Security (multi-factor authentication) app on your mobile device.

Note: Horizon.mmd.auburn.edu is used on campus. You must have a client to connect to horizon.mmd.auburn.edu; you cannot connect from the web.