You mean the white outline?
As you will find out there are several ways to accomplish the same thing.
You could duplicate the text and give the lower text a thick white stroke and the upper text the normal thin black stroke.
You could use layer styles using the stroke style and the outer glow style. Assign the outer glow to white with a normal blend mode and a fairly thick outline, then give the stroke a normal black thin line.
I know I am forgetting some but that should help.