h-1b Extension Stamping

Question on H-1B extension stamping :

 1) When i need the H-1B extension stamping ?

2) Do i have to go for visa stamping immediately after my H-1B extension?

 3) Travel outside US after H-1B Extension approval need a new stamping?

 https://www.youtube.com/watch?v=THr3CavQ4L8