Question

how the phase difference between current and voltage effects in the circuit??

Answer 1

If the current lags or leads the voltage, then you have your total power reduced than the value you would have if they were in phase. When the voltage and current are out of phase some of the power is dissipated in the inductive and capacitive element instead of a resistive element, which means loss for you as most of the times the output power is obtained across a resistive element

Answer 2

there are two kinds of power in electrical system, namely Active power and Reactive power. Active power is the one which does all useful work. When voltage and current are in phase the Active power is maximum, however if they are not in phase then that certainly means there exist a reactive power. Reactive power is due to Inductors and/or capacitors.

You can decide the nature of the circuit with the phase difference :
1. Inductive circuit : Current lags voltage.
2. Capacitive circuit : Current leads voltage.
3. Resistive : Current in phase with voltage.