Dependency Property

Hi,

i have used Dependency Property in my application but i unable to understand the significent of DP then normal .net property.

can any one explain to me about dependency property,attach property in real senarioes.

what is dependenecy property?
why we use dependency property?
when we use dependency property?
how we use dependency property?

what is the main advantage dependency property then normal .net property.

thanks

John