It means "listen" to the music.
it means you've zoned out. or a made up place and stop watching demi lovato La La land also references Hollywood . . .
Basically ooh la la is an exclamation of surprised approval. The expression may have very strong sexual connotations, but not necessarily. It is used in America and other places to indicate approval...
it means to "sing"
It means that you like something. For example,a boy likes a girl's dress and he says "I like your dress,ooh lala."