First lay your purse base flat (on the floor, on the table - anywhere you have a little room to work).
Lay your handle strip on top of it so it looks like this:
If you already have your handle to length and have stitched down the entire length of it, then you can mark the "middle" by making the "circle" of the handle flat, and then putting a pin at each end. These can be your "middles". You will then lay your handle on your purse, and put these "middles" in the middle of the purse between the pockets as seen here: (it's kind of hard to see the pins - :( )
So, better? A little more visual atleast.