How should I attach this sheet flooring?
Looks like vinyl flooring (appropriate for bath rooms). It most likely needs to be glued down. Be aware that some sheet material needs a special adhesive while others are glued by just applying adhesive to the perimeter of the sheet. look for the manufacturer's name on the bottom and check their web page for specifics.
Just a quick primer on installation: try to use a sheet for the full area (2 pieces are troublesome.
starting at the longest/most noticeable wall lay the sheet along it and push it into the room.
push it up to the bases of the toilet (if installed) and/or the vanity or pedestal sink.
you'll need to make a cut so that the vinyl sheet can be split around each side of the base.
Once the sheet is cut into the room half of it is pulled away from the floor and adhesive is troweled on the floor and the piece is returned and smoothed to the adhesive. Repeat on other half. Push air pockets out towards the perimeter with a rag.
You will most likely need an adhesive compatible with concrete floor. concrete