In this video

Install the door bracket to the top panel of your garage door. This bracket will be the attachment point for the opener's main arm. Once the door bracket is secured, connect the opener's curved arm to this bracket using the provided pin. The video demonstrates how the carriage (the piece that moves along the rail) has a lever that allows it to be engaged or disengaged from the door arm. When the lever is down, it's disengaged (for manual operation), and when it's up, it engages the door arm so the opener can move the door. This mechanism is useful for power outages or manual door operation.