Ptogwith corresponding cast on loop?

Hi i am fairly new to knitting and this is my first clothing project. It is a halter top but there is just one thing i am a bit confoogled about, do i do this with the purl sides together or the knit sides, i tried to do it last night and i got in a bit of a pickle, any advice would be really appreciated!
many thanks,
big hugs,
Bethxx

Assuming that you’re creating a hem at the bottom, I think you would do the “P2tog with corresponding cast on loop” with the purl sides together.