When studying the molecular nature of electricity it is necessary to consider the true direction of electron flow negative to positive.
For all electrical applications the direction of flow can be considered in either direction, but in most diagrams we use conventional flow positive to negative. i.e bus bar, consumer, earth.
Current flow is not often regarded as important it is when it stops that is the problem and requires action.
When a current flow is induced using magnets and coils the generator will always be spinning around. The phase of this induced voltage will alternate between a negative and positive polarity each 360 degree revolution. 90 degrees being the peak positive voltage. Zero and 180 degrees being zero volts. 270 degrees being peak negative voltage.
When rectifying this produced wave the diode or bank of diodes will only allow the voltage to go one way and not the other like a non return valve. This produces a Direct one way current or rectified current.
Hope this gets you started.
B