First you need your FTP details, you can find them using this guide: Accessing your FTP Details
Once you've got those details you're good to open Transmit and you should be met with a similar screen:
You'll need to change SFTP to FTP with TLS/SSL
Make sure Passive Mode is ticked
Once that's done just fill out the FTP info with the server IP, Username and Password
Hit Connect, if you get this message just click Continue
After that you should be connected and greeted with this screen
