how is resistance created when electrons collide with each other?i need a simple explanation

There is always some obstruction to the flow of current when current flows through a conductor like metal wire.This obstruction offered to the flow of current is called electrical resistance..

The flow of current in a wire is due to the movement of electrons through it. The metal wire has free electrons which move in random manner in absence of any cell connected across it. When the ends of the metal wire are connected to a cell, the electrons start moving from the negative terminal of the cell to its positive terminal through the metal wire. During their movement they collide with the fixed positive ions of the wire due to which they loose their speed and change the direction of motion. But after collision electrons again accelerate towards the positive terminal.They suffer collision with the positive ions again and again. As a result the electrons do not move in bulk with an increasing speed, but they drift towards the positive terminal. Thus the metal wire offers some resistance to the flow of electrons(current) through it.