If you stand in front of the car and you have the
lever arm above the square hole attachment point
you then pull the lever towards you.
You are pulling againist a spring so you must hold force on
the lever the whole time. Pull gently but frimly till it stops
and hold it there and now remove belt.
Once the belt is off you can slowly reduce tension.
depending on the tool you are using you may find that the small
hose (3/4" diamater or so) from the coolant recovery bottle is
in the way of your lever. I found this to be the case as the
tensioner with no belt in place will rotate farther than if a belt
were in place. I temporarily used some wire to hold the tool
I used in the full forward position while I got the old belt off
and new one on.

I have seen the vise grip and 3 coins picture. I keep that idea
in the back of my mind in case I am stranded some time, but
decided to make a tool from a piece of flat stock, a piece of 3/4" square
bar stock and two socket head cap screws.
I would think that if one had the right width flat stock and could heat it
up to bend it it could be a one piece tool.

I have seen IPD selling one for approx 30$us plus around 10$us for us
shipping and decided to make my own instead.

ascii art of the tool I made,
top view
___________________________________________

                                        | |
                                        | |
                                         -
front view
___________________________________________

hope this conveys the message as you can see I am not skilled
at ascii art.

Can one attach very small jpgs in this newsgroup to show a point
like this clearly???