How do I set up CT Raid Assist addon?

If you have CT_RaidAssist and CT_RABossMods installed you should have a new icon on your minimap -> (RA).
Click on this icon and choose "Open Options" A window will pop up on your screen. Choose "General Options"
Be sure that "Display Main Tanks" is enabled.
Click Back and choose "Misc Options"
In "Notifications" panel check "Notify on aggro gain" with "play sound" in "Display" panel check "Display MT's Target's Target" (you will now when to lay off dps - very useful for boss fights).
Click Back. Choose "Additional Options" and check "Show emergency monitor" (very useful for healers)

Those are the most important features but this addon is much more complex than that. You should read the help for the rest of the options.

This Q&A was found on The Order of Azeroth Guild Site - New server : http://www.theorderofazeroth.net/modules/smartfaq/faq.php?faqid=3