Without question, the major appeal of flat panel televisions is its form factor. Being able to wall-mount a set maximises the visual appeal, but mounting to plasterboard (with presumably metal studs) is not as straightforward.
Examine the plasterboard using the stud finder. Determine the separation between studs. Drill a small test hole to determine the stud material using the 1/4-inch bit.
Cut the 2x4 plank to the same width as the part of the wall bracket that will sit against the wall. Place this against the wall flat, and use a pencil to trace around it.
Cut out the plasterboard using the drywall knife, so the 2x4 fits into this new opening. Since most metal studs are 2 inches thick, this should place the 2x4 piece virtually flush with the plasterboard.
Drill through the 2x4 plank and into the concrete/brick behind it, creating four holes. Ensure these holes will not eventually interfere with the bracket's bolts.
Drill the tapcons through the 2x4 and into the substrate behind it. Give a few firm tugs to ensure stability.
Place the wall mount over the installed 2x4, and mark at least two lag bolt locations with a pencil. Pre-drill these spots with the 1/2-inch masonry bit into the substrate.
Mount the wall bracket to the 2x4, using the 4-inch lag bolts, washers and socket wrench. Check alignment with a level.
Mount the TV side of the wall bracket to the set, using the appropriate screwdriver and screws.
Mount the TV to the wall bracket.