Resistance—
The resistance of a conductor is the property by virtue of which it opposes the flow of charge through it.
It is equal to the ratio of the potential difference applied across the conductor to the current flowing through it.
Its unit is Ohm or Volt/Ampere.
Definition of One ohm—
If V=1 Volt i=1 Amp then
R= 1 ohm
Electromagnetic Force—
The emf of a source is equal to the maximum potential difference between its terminals when it is in open circuit that is when it is not sending any current in the circuit.
The emf of a source is defined as the energy supplied by the source in taking a unit positive charge once round the complete circuit.
Kirchhoff’s Laws—
Kirchhoff gave two laws
Kirchhoff’s First law or Junction Law or Kirchhoff’s Current Law (KCL)
This law states that at a junction, the algebraic sum of all the currents is zero. In other words at a junction the sum of all the incoming currents is equal to the sum of all the outgoing currents.
Electric Energy—
The energy of a voltage source to flow a constant current through a resistor for a given time is called Electric Energy consumed in the circuit.
Let a voltage source ‘V’ supplies current ‘I’ through a resistor ‘R’, then 
The unit of Electrical Energy is ‘Watt-second’.