They require a dedicated 240-volt electricity supply. Almost certainly, if you look at an outlet in your home or office right now, there will be one on top and one on the bottom. Even though the total voltage provided is 240 volts, these standard outlets in the home are typically 120 volts each.
Leaving an electric vehicle plugged in is almost always risk-free. All electric cars have safety features to prevent the battery from being overcharged. It's cool to leave it plugged in, then.
The first-come, first-served principle applies to public charging stations. During a charging session, never disconnect a connector from another electric vehicle to avoid damaging the charger or the car.
In recent years, manufacturers have improved EV battery protection to lower the possibility of fire or explosion in the event of a collision. Some fires start while being charged, like the ones that have been in the news lately, leading to safety recalls that will cost billions of dollars.