Let's see, how to tell it...

He laid 2 screens end to end, and tacked the screens onto the frames at
the far ends. Stand by for bad ASCII art:

|~~~~~~~~~~~~~| |~~~~~~~~~~~~|
| | | |
|~~~~~~~~~~~~~| |~~~~~~~~~~~~|
Here and Here

Then, put a 2x or something between the 2 frames, effectively making
the total length of the actual screen material longer and stretching it
tight. Proceed with nailing it down.

I hope that clears it up.

-Phil Crow