section of Home Depot. I forget the mil thickness, but its about 20 typing sheets thick. This stuff is the first water barrier of your shower floor pan.
When I re did my shower stall due to a cracked pan.
I stripped out the tile, took out what was used 30 years ago, green board, then hammer out the cement bowl shaped (concave) pan. Then I got to the liner. It was torn and compromised.
I got new liner, cut a hole for the drain pipe, which was in the middle of the membrane, then took the membrane up 1/2 half up the sides of the walls. What you have to be careful about is the folds. This stuff is soo thick that folds can mess up the hang of the cementious board and make the tile setting more difficult.
Cutting the membrane is a no no. Alot do it because its the easy way and the homeowner probably does not know about it or sees it. Do tucks instead of folds and have the tuck back into the wall. This way the membrane is box shaped and makes the cementious board go up nicely.
When fixing the membrane to the wall studs, use the special rubber attached nails for a good seal.
Remember, the standard is the membrane up one third from the floor, but I think higher is better and you only do this once. Leaks occur in showers where the force of the shower head directs the water to the opposite wall. If your six feet tall the water will be directed about mid chest, so that could be 4 to 5 foot. When you walk away the force is on that corner that height.
Now, install your cementious board all the way around and up. Be sure to install the right side in and right side out. There is one right way.
Cut this stuff with a circular saw and an old blade that you will not use again and watch out for all the dust.
This should get you going for a while and then come back with new questions as you go.