Place your stud finder against the wall. Locate a space that is wide enough for the speaker, in between the studs -- the vertical boards in the wall. The sensor will light up when you hit a stud. Mark the end of the stud with a pencil, and then move to the right to find the next stud. Mark this end as well.
Place the in-wall speaker wall template against the wall, in between the two studs. Use a level to make sure it is straight, and then tape the template to the wall with masking tape.
Draw an outline around the template with a pencil. This will make it easier to cut the required hole in the wall.
Remove the wall template, and cut the outline out of the wall with a drywall saw. Take your time, because if you mess up the wall, it will require additional repairs. When finished, save the piece of drywall you have removed, in case you need to make repairs later.
Install the mounting bracket that comes with the speaker system, fitting it snugly inside the hole. When the speaker is mounted to the wall, it will be held in place between the speaker system and the side of the wall. Screws are usually not necessary at this time.
Drop the wires for the speaker system through the hole you created in the wall. Drill a hole in the base of the wall with a 1/2-inch drill. Pull the wires through the hole and string them along the baseboards to your stereo system. When finished, you can hide the cords by removing and replacing the baseboards. Alternatively, attach the cords to the base of the wall with metal braces and then paint the cords to match the wall.
Place the speaker into the wall. Using an appropriate flat-head or Phillips screwdriver, depending on what type of screws are supplied with your system, screw the mounting bracket screws into the wall. Do not use an electric screwdriver, since you can easily break the backing.