100 MV Lightning is formed form a buildup of charge in the atmosphere. It build up charge from the static from water droplets. This causes a charged cloud. This charged cloud induces an oppositely charged surface on the earth. This path is lower in resistance than the surrounding air and charge flows through this channel, creating lightning.
Electricity is the flow of charge.
The current is the amount of charge that flows through a cross-sectional area in one second. Voltage is the work done per charge. The voltage of lightning varies with certain altitudes and thickness of the bolt. These fluctuating values are caused by the fact that the cloud and earth act as capacitors. A capacitor is a device used to store charge.