Question

My teacher has taught me that Convex Polygon :-we get a convex polygon if its angle is less than 180 degree. Concave polygon:-if any angel of polygon is greater than 180 degree. IS THIS RIGHT OR WRONG PLEASE TELL ME.

Answer 1

It is right. But the only point to add is that the angles  which are being referred to are interior angles of the polygon.
A convex polygon is one which has all of its interior angles less than 180°.
A concave polygon is one which has at least one of its interior angles greater than 180°.