Take a look at My Master Bathroom Shower that I re-tiled. I have pictures of some of the steps. First the membrane goes down. The mortar bed goes on top of the membrane and the tiles on top of the mortar bed. It cost about $300 to get a plumber out to reset my drain, install a metal flange, and set the membrane. I had an old lead drain pipe that had to be cut free from about a 300 pound concrete shower pan. That thing was heavy! Since I was a bit sure of the procedure for doing the mortar bed, i hired a tile guy for $100 to lay the bed. I did all the rest of the work.