The first step is to snap chalk lines onto the floor to mark the dimensions of the sheets. You want to be sure that your joints don't line up with the joints on your sub-floor and so that there is nowhere four corners of backer come together.
Starting in the furthest corner from the door, spread enough thin set onto the floor for one sheet of cement board.
Once you've filled the space, make ridges in the thin set with the a notched trowel. Lay your first piece of backerboard in place leave a quarter inch gap between the board and the wall.
To cut cement board, score the board with a utility knife or carbide tipped cutter, and snap on the score line. For outlets or toilet flanges, trace and then drill holes in the perimeter, score lines and snap out small pieces.
Repeat the process until the floor is covered; leave an eighth of a inch seam between boards.
Once all of the boards are in place, secure them to the floor with backerboard screws every eight inches, along the outside keep screws between a half an inch and two inches from the edge.
Once everything is secure, fill the joints with adhesive, extending it out from the joints about an inch and a half on either side.
Lay two inch fiberglass tape over the joint pushing it into the adhesive. When it's in place cover the tape with a thin layer of adhesive feathering it out at the edges.
That's it, ready for tile! I'm Mrs. Fixit and it's just that simple!