In 1974 Vinton Cerf and Robert Kahn published TCP/IP: instead of holding open one dedicated wire between two computers, a message is chopped into small packets, each stamped with its destination and set loose independently.
That is packet switching. A circuit-switched phone call reserves a whole line end to end; packet switching lets thousands of messages share the same roads, each packet forwarded on its own.
No packet carries a map. At every junction a router reads only "the shortest way to this address is that link" and hands the packet on — a local decision, repeated hop by hop, with no central controller to fail.
Packets can take different roads and arrive out of order; TCP numbers them and puts them back in sequence, and retransmits any that are lost. But a link is not infinite: fill its buffer and packets are dropped — that is congestion.
Something in the simulation stopped unexpectedly — the lesson continues without it. You can move on; nothing you did was wrong.