Voltage across a cell or power supply is the energy given in to each coulomb. It's measured in volts, and the symbol in a circuit is V. It's measured using a voltmeter.
Electric current is the flow of charge, going from positive to negative. It has the same value at all points in a series circuit, but the amount depends on the amount of power in the circuit- the number of cells. It's measured in coulombs per second, or amps, using an ammeter.
Electric charge is measured in coulombs, but not often directly.
Resistance is measured in ohms, and is higher the longer or thinner the wire is, and depends on the material. The higher the resistance is, the lower the electrical current is if the voltage stays the same. A short circuit is a short cut that has a lower resistance the circuit.
Conductors are, by definition, materials which conduct electiricity well- most metals are good conductors, copper being the prime example. Copper is used in wires and because of its ability to conduct electricity well.
An insulator is a substance that doesn't conduct electricity, but instead blocks the flow. Rubber, paper and wood are all good examples. Rubber is used on the outside of wires and on plugs for electrical safety.
Circuit diagrams are used to represent the circuit set up in an experiment in a simpler way which is easier to read.
Plugs have to be made in a specific way so they are safe. The neutral wire is the one which actually takes the electricity into the ground, whereas the live wire is the one you don't want to touch under any circumstances- the repercussions could be painful. The earth wire is the one that takes the electricity back to the main electrical panel in case of a fault.