Question

What's rotational symmetry, how to find its order?

Answer 1

In rotational symmetry,the shape or image looks same also after it is rotated.How many matches are there as you go once is called the Order. 

Answer 2

In Rotational Symmetry the shape or image can be rotated which still looks the same.  

To find its order:  We have to see how many times it looks like itself when we rotate it 360 degree. Eg: A square looks like it was originally was 4 times when we rotate it by 360 degree and hence a square has 4 rotational symmetry. Whereas a rectangle originally looks like it was originally twice. And hence it has 2 rotational symmetry.