HOW CIDR SIMPLIFING THE WORK OF ROUTING TABLE?

That is a good question and the answer is a CCNP topic called route summarization. Lets say that you have 2 subnets bound on 2 ethernet interfaces. The first 192.168.0.1/24 and on the second eithernet interface, 192.168.1.1/24. Weill instead of advertising 2 seperate routes on your routing table, you would simply just advertise a summary route of 192.168.0.0/23. This would essential advertise both individual subnets as one route and then as the packet arrives at the route via your serial interface, the router would route the packet to the correct ethernet interface based on its binding and the IP address of the packet.