35mm Camera Explained Self Portraits With 35mm Camera...?

Self Portraits with 35mm camera...? - 35mm camera explained

Well, my photo teacher explained to me shortly, but I do not understand ... I try to make themselves portraits. I have a 35mm camera, so I'm with the timer and I have manual focus in advance. The approach is part of the problems that I feel.
You mentioned something before about Focus, where I am, and then back, then you will find the point between the two. This makes sense for me, but how do I do if I stand in front of the surface is said, only a wall. This is not only the wall behind me, no point of me.

Materials ... Camera with a timer, a tripod, cable release (I know the trigger flash cable ...), it would be nice.

Suggestions? In addition, all sites that are explained, this would be greatly appreciated!

Thank you.