Meaning no offence but asking these questions make me wonder if you have read the manual?
Indcidentally and from experience, it is rather risky to fly with the obstacle avoidance On whilst in confined spaces, indoors or outdoors, especially if the drone is new to you and you do not know what the indications mean.
As I said, that is from experience, meaning I have done the same thing myself, my bad, it nearly cost me an M2P.