They really should explain it somewhere 
On the seat back in front of you is a little flap velcroed down with a sign that says something like for iPad only. If you lift it up, you'll find it's sticking to a strip of fabric sewn at either end to the chair, making a loop just wide enough for an iPad.
The front cover of the iPad is heavy enough that if you slide it through the loop, the iPad stays there as if it were an in flight entertainment screen. Then re-attach the flap using the velcro just to make sure it doesn't move.
On the seat back in front of you is a little flap velcroed down with a sign that says something like for iPad only. If you lift it up, you'll find it's sticking to a strip of fabric sewn at either end to the chair, making a loop just wide enough for an iPad.
The front cover of the iPad is heavy enough that if you slide it through the loop, the iPad stays there as if it were an in flight entertainment screen. Then re-attach the flap using the velcro just to make sure it doesn't move.