postDelayed

I have a couple questions about postDelayed, see context below.

1. What is postDelayed?
2. What is it used for?
3. When should it be used? In other wods, in what circumstances should it be used?
4. What is "new Runnable()"?
5. Don't you have to declare a Runnable variable first? e.x. Runnable r = new Runnable()
6. What is public void run() if it never gets called. In other words, what's the point of creating a "run" method if it never gets called explicitly. Does it get called implicitly somewhere?

public void onClick(View v)
{
    ToggleButton.postDelayed(new Runnable()
       {
           public void run()
           {
              // do something
           }
        }
}