I dont know if ? can explain it clearly,so sorry !
this slipper is started as a basic toe up sock.but you must use both cards in the same time.also,for example:
round 1:read from first card row 1 and in end of row follow the second card and read row 1. (of course dont forget the increase stitches .Increases can make as kfb :knit forth and back in the same stitch )
If you have questions, please do not hesitate to ask me.

My pattern need more explanation and test knitting.Its writting in one size.(EU 38 SHOES?ZE)