Resistance is the measure of opposition to the current flow offered by the material.Usually denoted by R. Resistance is when voltage & current stay in phase, and it follows basic Ohms law. It is considered as 'real'.
Reactance is the resistance offered to the ac currents by inductors and capacitors only. Usually denoted by X.
For capacitors X=1/(2πfC); where f is the frequency,C is the capacitance.
For inductors X= 2πfL; where f is the frequency,:L is the inductance.
Reactance is when Voltage & current are 90deg out of phase. Depending on whether it is +90 (lead) or -90 (lag) it is called an inductive reactance or capacitive reactance. Reactance is normally denoted by the imaginary operator 'j' .
Impedance is the sum of the resistance and reactance of a circuit denoted by Z=R+jX (for primarily inductive cirucits) or Z=R-jX (for primarily capacitive circuits).
It is usually represented as a complex number like 2 - j3.5. The phase angle between V & I could be any value.