Equality of sets is defined as set is said to be equal to set if both sets have the same elements or members of the sets, i.e. if each element of set is also belongs to each element of set as well as each element of set is also belongs to each element of set .
Mathematically it can be written as and in this case we write as . If there is at least one elements of which is not in , then is not equal to and we write .
For Example:

Let and , then because each elements of set that is is equal to each element of set that is . If we rearrange the elements the sets it will be remain same.

Let and , then .