What are these holes in my concrete wall and how can I mount things to them?
Using these holes for a mount is feasible if you can use two or more of the holes for one rail. 

One method is to make round wooden plugs that just fit into the holes. Make it so it can go in as deep as possible whilest not sticking out beyond the surface of the wall.

Next you cut the plug in half as shown below. Place the two halves of the plug into the hole and then pound in some wedges to make the plug fit into the hole as tight as possible. Be careful to use a wedge that does not have too much angle to it so that you can get expansion of the plug as far down in as possible. 



After the thing is wedged in place cut off the excess length of the wedge. The plug can now be used as a screw point to mount a flat plank across the wall. It would be to this plank that you mount any additional harware for the monitor mount.