packetizing: encapsulating the payload in a network-layer packet at the source and decapsulating the payload from the network-layer packet at the destination.

Routing: there is more than one route from the source to the destination, the network layer is responsible for finding the best one.

Forwarding: The action applied by each router when a packet arrives at one of its interfaces. A router normally use a decision-making table for applying this action. It is called (the forwarding table) or (the routing table).

From I mentioned above what do you understand?