Tape strips of foil around the cardboard. Tape a clip wire to each of the pieces of foil. Join the wires in a circuit with the battery and the buzzer. Set up the burglar alarm near a door so that anyone coming through the door will step on the cardboard and set off the buzzer. The flow of electricity through the electric buzzer causes it to make noise.
Voltage is electrical pressure or force.
Current is the flow of electrons passing a given point. Power is the work performed by a current. We generate voltage by using batteries, generators and solar cells. We get current by placing voltages across things such as buzzers, lights, resistors and other interesting devices. Using voltage to make things happen is the purpose of electronics.