Short version

extends means:

The new class is a child. It gets benefits coming with inheritance. It has all the properties and methods of its parent. It can override some of these and implement new ones, but the parent stuff is already included.

implements means:

The new class can be treated as the same "shape", but it is not a child. It could be passed to any method where Person is required, regardless of having a different parent than Person.

Long version 

check the source