The manual changeover switch is wired into your electrical distribution board (DB) in your premises allowing it to power to everything or just specific circuits if wired this way.
The generator does require time to get up to speed before the manual changeover switch can be placed on "Generator." The recommended time for this is 30 seconds. The generator should be started whilst the manual changeover switch is in the "Off" or neutral position. Once the generator has started started and run for the recommended time the switch can be moved to "Generator" or "Gen" position to provide power.
The manual changeover switch has 2 lights built into it that indicate the presence of power either from the mains electricity provider or the generator. A buzzer or siren can also be fitted to the manual switch in order to give the user an audio queue once mains electricity is restored. A buzzer or siren is an additional extra.
When you choose to use a Manual switch you need to ensure that the battery is kept charged up for when needed. Ideally you need to have a trickle charger installed with the switch in order to keep the battery topped up for when you have a power outage.
Various sizes available in single and three phase. You should always size the manual switch based on the largest load that will be put through the switch.