While I do not plan to mount a TV in my bedroom, if I were to ...
The magnet is used to find stud. You can also use an electronic stud finder which will find either wood or metal studs.
The backer supplied by the factory is not metal (to the best of my knowledge). It would be a thin piece of plywood or something similar.
Determine if there is a stud where you wish to mount your TV. Mark location with a piece of masking tape.
Get a piece of 1/4 or 3/8 plywood, 8X10 inches would work or slightly larger. Paint to match wall.
The plywood will be centered right to left behind your TV. Top to bottom location depends upon your mount. If there is a stud located behind where your TV will go, put 3
sheet metal screws through the plywood into the stud (spaced vertically in the plywood)--AFTER the next step.
Drill 4 holes located near the corners of the plywood. Hold the plywood in its location and mark through the holes with a nail to indicate their position on the wall. Remove the plywood, install 4 wall anchors where the marks are. Put the plywood back in place and fasten with the wall anchor screws. Then put in the sheet metal screws through the plywood into the studs.
Fasten the TV mount to the plywood with the 4 supplied screws. Fasten the plate to the back of the TV with the supplied bolts.
Install all cables to the back of the TV--power, HDMI if you will need one, and cables for signal.
Connect TV to wall mount.
If you use an articulating mount that will let you swing the TV away from the wall, you will increase the possibility of the TV ripping the screws out of the wall at some time.
I recommend using a simple mount that will hold the TV close to the wall or one that will let it swivel slightly. Best Buy and similar stores do not usually carry these mounts because they are so inexpensive. Look online for TV mounts, should be less than $20.
First choice--get your dealer to mount the TV
Second choice--stop by a Camping World on a trip, buy a mount from them and get them to mount it for $39
Third choice--above
Robert