What does “implements” do on a class?

Question

If a class implements another class... what does that mean? I found this code sample: http://www.java2s.com/Code/Php/Class/extendsandimplement.htm

But unfortunately

Answer 1

An interface defines a simple contract of methods all implementing classes must implement. When a class implements an interface, it must provide implementations for all its methods.

I guess the poster assumes a certain level of knowledge about the language.