If a car or a train moves, it causes all the cars of the train to move by the same amount, and free electrons in the wire act in the same manner. the free electron is always present throughout a wire, and as each electron moves slightly it exerts a force on the next electron, causing it to moves slightly intern to exert a force on the next electron. this effect continues throughout the wire.

When electrons move away from one end of a wire it becomes positively charged, causing all the free electrons in the wire to move in that direction. this movement, taking place throughout the wire simultaneously, moves electrons away from the other end of the wire and allowed more electrons to enter the wire at that point. 

Since electrons repel each other and are attracted by the positive charge, they always tend to move from a point having an excess of electrons toward a point having a lack of electrons.  your study of the discharge of static charge showed that, when a positive charge is connected to a negative charge, the excess electrons of the negative charge move toward the negative charge.

if electronics are taken out of one end of a copper wire, a positive charge results, causing the free electrons in the wire to move toward that end. if electrons are furnished to the opposite end of the wire, causing it to be charged negatively, a continuous movement of electrons will take place from the negatively charged end of the wire toward the positive charge end. this movement of electrons is current flow and will continue as long as electrons are furnished to one end of the wire and removed from another end.

Current flow can take place in another material were "free" electron exits, although we are only interested in the current flow in metal wire.

The direction of current flow:-

According to the electron theory, current flow is always from a (-)negative charge to a (+)positive charge. tush, if a connection between the terminals of a battery, current will from the   (-)negative terminal to a (+)positive terminal.

Before the electron theory of the matter had been worked out, electricity was in use to operate light, motors, etc .electricity has been harnessed but no one knows how it is work. it was beliving that something move in the wire from  (-)negative terminal to a (+)positive terminal. this conception of current flow is called conventional current flow.  although the electron theory of current  (-)negative terminal to a (+)positive terminal is the accepted theory, you will find the conventional current flow + to - sometimes used in working with certain types of electrical pieces of equipment.