1) An electric circuit is a complete path that allows electric current to flow. A battery acts as a pump to push current through the circuit. 2) There are two basic types of circuits: series circuits where current flows through components one after another, and parallel circuits where current divides among branches. 3) Circuit diagrams use symbols to represent components and show connections using straight lines meeting at right angles. Voltmeters measure voltage in parallel, ammeters measure current in series. Fuses and circuit breakers prevent overloading.