Who ever told you that was probably refering to the section just under axis a, axis b, ellipse, etc.
Click on the box to the right of where it says "Activation". In the pull down select "East".
In the row just below that there are three options. Starting from the left they are. "present", "not present" and "detected by west". click on the middle one. make sure your axis a and axis b are set large enough to cover the area that you want covered.
In the third section of the trigger (from the top) click on the box to the right of "Type". From the pull down select "end #1". (if that's the ending you want to trigger)
Attached is a screenshot of how you want the trigger set up. (except for end #1. I forgot that!)
mcnorth