Can anybody teach me the concept of current and voltage with their differences?

Current is the rate of flow of charge. I=Q/t where I is current and is measured in Amperes A, Q is the charge and is measured in Coulombs C and t is time in seconds s. So current is how fast or slow, charged particles(ions, electrons) flow through a conductor. In a circuit for example you can have a current of 4 A, that is 4C of charge passing from a point each second. Voltage is the energy transferred per coulomb of charge. V= E/Q, where V is the voltage in Volts V, E is the energy transferred in Joules J and Q is charge in Coulombs. Batteries act as 'electron pumps', as they transfer chemical energy into electrical. A battery of 5V will convert 5J of chemical energy to electrical each time a Coulomb of charge passes across the component.

Iagree c would be the answer