you need to be more specific as to what you want. have you tried google or wikipedia?
basically, the intersection of two or more sets is the set of elements that are common to each and every set.
the union is the set of all elements in all the sets, whether they are in common or not.
example: let and
then the intersection is: , since those are the elements the sets have in common
and the union is:
If we had a third set,
then
and