Photoshop cs5 help with layers

[atspac la faza]

Hi guys i just saw this art section and i wanna ask you a question about photoshop cs5, how can i unite a layer with another one like in this video
http://www.youtube.com/watch?v=3cCIV7-Ao4o at the momente 00:31 you can see at the right, that the layer background have been united with the layer 1, but i think he used some quick buttons and it don't shows on screen... just tell me how can i do that, thanks
Sorry if i'm in the wrong section.

[Crotale]

You can right-click on the top layer and select "Merge Visible" or "Flatten Image." The Layer context menu up on the upper menu bar has the same functions available.