Why cant I see the loop cut line on one side of the mirrored shape I'm new, so this may sound stupid. 

When I make a loop cut, I can see where it is on the original side, but not the mirrored side. Is there some option or setting I need to change in order to fix that?
There are two options to display the result of the modifier in edit mode:

(form the Blender Manual)

Box
Displays the modified geometry in edit mode, as well as the original geometry which you can edit.
Triangle
When enabled, the final modified geometry will be shown in edit mode and can be edited directly.

Enabling the triangle will allow you to &quot;adjust edit cage to modifier result&quot; :