What are the differences between the two?
Can anybody give an special example (and rarely known, if possible) for that?
I have no idea why you want a rare example. How do you learn from that?
If n is evenly divisible by 10, then, necessarily, n is evenly divisible by 2.
But it is false that if n is evenly divisible by 2, then, necessarily, n is evenly divisible by 10.
So the first statement is an example of an "if" statement. It is necessarily true in only one direction.
If n is evenly divisible by 10, then, necessarily, n is evenly divisible by both 2 and 5.
If n is evenly divisible by both 2 and 5, then, necessarily, n is evenly divisible by 10.
Those are examples of "iff" statements; they are necessarily true in either direction.