Sure, I will try to guide you.
Basically, what you're going to want to do is create some type of control. Can be anything. I usually use a locator, control box, or a custom nurbs curve shape.
Anyway, position the control behind the elbow while in it's default pose.
With the control still selected, select that arm's IK Handle. Within the Animation Toolbar, select:
Constrain -> Pole Vector Options Box
In the Options Box, you probably won't have to adjust the weight very much. In this case, since it looks to be a human arm, try something between 0.05 and 0.1, which is a safe bet.
Then, it is basically done. If you have a bend in the arm, and the control is properly placed, the elbow should move up and down with the control. The IK Handle can still be used to move the arm around in any fashion, but the elbow will stay pointed at it's control. This way, you can move the arm around, and position the elbow manually.
I hope this helps!