Difference of set A and B means
all elements of set A which are not in B
Let A = {1, 2, 3, 4 } , B = { 3, 4 , 5, 6}
A – B = {1, 2}
The blue region is A – B
For B – A
B – A = { 3, 4 , 5, 6} – {1, 2, 3, 4 }
B – A = {5, 6}
As B – A = All elements of B which are not in A