It is measured in Volts. Resistance is a measure of a material's ability to oppose the flow of electricity. It is measured in Ohms. These formulas are handy, since often you're given two pieces of information about a circuit or component and you need to figure out a third piece of information. Components Conductors are materials through which electrical current moves freely.
Insulators are materials which prevent the flow of electricity.
Resistors resist, but do not totally block, the flow of electricity. They are used to control the flow of current. Current can move either way through a resistor, so it doesn't matter which way they're connected in a circuit. Sometimes they are polarized, meaning current can only flow through them in a specific direction,and sometimes they are not. If a capacitor is polarized, it will be marked as such on the diagram.