et en plus tu as une ambiance formidable avec la danse et la musique. This phrase in your course is translated as "and plus there is a........ I thought "there is or there are" was translated as il y a not tu as.

There'd be nothing wrong with saying "et en plus il y a une ambiance", in this case "tu as" (iterally meaning "you have"), is clearly another colloquial way of putting it. In fact, if they'd translated it as " and plus you have a . . ." it would've been understood to mean exactly the same thing. Judging by the age of this post, I'd guess you've figured out this one by now, so we'll just leave it here for anyone else with the same Q. :o)