There is a parade, concert (who is playing won't be announced for months, but they tend to get a few big names to play), Louisiana style food, etc. It isn't a separate ticket event like HHN, it's usually pretty fun but nothing to write home about.
I haven't been yet (plan to the end of Feb 2016), but from what I gather from last year's schedule it looks like it starts the first weekend in February and goes through mid April. I think the concerts and parade are only on Saturdays during this time period. Hopefully someone will correct me if I'm wrong. Here's a media release announcing last year's mardi gras events - https://media.universalorlando.com/PressRelease/detail.aspx?id=50729&ct=27752