Why can't I find seating chart,is it first come first setting serve?

Yes

IMAX is reserved seating, others are not.

Most theatres are first come, but there are a couple that are reserved seating

The rows are marked on the outside of the row and seat number is on the arm rest. I subscribe to the first-come - first seated theory but then you get some uppity people who ruin it, showing up 10 minutes into the movie saying "you're in our seats" so prepare for that too.