A NAND gate can have two or more inputs. The o on the output means not showing that it is a Not AND gate. The output of a NAND gate is true unless all its inputs are true.
Electricity is the flow of charge around a circuit carrying energy from the battery (or power supply) to components such as lamps and motors.
Relay An electrically operated switch, for example a 9V battery circuit connected to the coil can switch an AC mains circuit. The rectangle represents the coil. NO = Normally Open, COM = Common, NC = Normally Closed.
Preset variable resistor A preset is operated with a small screwdriver or similar tool. It is designed to be set when the circuit is made and then left without further adjustment. Presets are cheaper than standard variable resistors so they are sometimes used in projects to reduce the cost.