I am wondering that how can current be equal on either side of a resistor as the work of a resistor is to resist the flow of electrons i.e. decrease the current. How is this possible?
The term decrease in resistors decrease current doesn't mean the outflow is smaller than the inflow. It means the flow through that entire channel/pipe/wire is smaller with the resistor than without.
It's probably more accurate to think of a resistor as impeding or restricting current. Like a kink in an air hose or water hose. The flow just before & just after the kink will be smaller than without the resistor. But the same amount of stuff that flows into the kink/resistor also flows out; otherwise stuff would be accumulating inside the resistor.
Charge is a conserved quantity. If charge flows into a resistor at 1 charge unit per second, it must also flow out at 1 charge unit per second.
Liken the circuit/resistor system to a smooth tile floor where one of the tiles has been covered in sandpaper. Now imagine you have a bunch of wood blocks all attached to each other with rope to form a chain of wood blocks, and you are dragging this chain of wood blocks across the floor.
There's going to be friction between the sandpaper part of the floor and whatever block is being dragged across it at that time, but all of the blocks still move at the speed with which you are dragging them. That's kind of how it is in a circuit.