What happens next?

How to install a car stereo
Set the parking brake and disconnect the negative cable from your car battery.
Be sure to do this to avoid short-circuiting the electrical system during the installation.
For instructions on disconnecting the battery, see how to disconnect a car battery.

Available options: I. Disconnect the battery if using a manual transmission transmission. Not all modern vehicles have the capability to remove a battery if using the manual transmission. II. Locate a flat, grass surface, like a driveway. It's better to have smooth, level ground instead of moist pavement. III. Unscrew any screws that are securing the trim in place. Be careful to remove all screws before trying to pry off the trim or you may break it. IV. Before you begin, refer to the vehicle owner's manual. Some vehicles have built-in parking brakes attached to other vehicles.
III.