Problems understanding instructions

Maravill has asked about the same instructions, but I still do not understand why the instructions : on 1st row instructions, it has P2 (1-6-5-1-5) isthe the number of pearl stiches for different sizes or sets of P2’s. this is relationship to different sizes of sweater or knitting needle being used. I knitt a Pearl 2 times and if I chose a medium size I only do 1 Pearl? This makes no sense to me.

For these instructions, you’d either purl 2, [I]or[/I] purl 1, [I]or[/I] purl 6, [I]or[/I] 5, [I]or[/I] 1 [I]or[/I] 5, depending on your size.