Voltage and Current:

Like static electricity, electrons can be motivated to flow through a conductor. The force is the same force manifested in static electricity.

When electrons moves through a closed path then it is called a circuit. When the specific potential energy is different in two location of a circuit then electron flow from high potential to low potential. The measure of specific potential energy (potential energy per unit charge) between two locations at a circuit is called voltage. Voltage is an expression of potential energy. Hence it is always relative between two locations, or points. Most of the time it is called a voltage "drop."

 

If we connect a voltage source to a circuit, then because of the potential difference, electrons will flow uniformly through that circuit. This uniform flow of electrons is called current.

The amount of current is always same at a single loop circuit. The current will not change anywhere in the circuit. But the voltage drop will be different. 

In a broken circuit, where there is a voltage source connected, then the full voltage of that source will appear across the points of the break.

The + sign shows the positive polarity in a circuit and the - sign shows the negative polarity. This convention is also relative.