Packaging is putting the chip into it's package, which is the board it's directly attached to. For CPUs, there's not much more to it, just attaching the heat spreader and etching it.
GPUs are a bit more involved since they go on a full board with memory, capacitors, and the like. But packaging is the most complex part after chip production itself (and the design process, but that is already happening outside of SE Asia). Think of all of the connections on a CPU socket and consider that the chips themselves are smaller than that socket. You need to solder each of those connections simultaneously without shorting them out to their neighbours.
Packaging is putting the chip into it's package, which is the board it's directly attached to. For CPUs, there's not much more to it, just attaching the heat spreader and etching it.
GPUs are a bit more involved since they go on a full board with memory, capacitors, and the like. But packaging is the most complex part after chip production itself (and the design process, but that is already happening outside of SE Asia). Think of all of the connections on a CPU socket and consider that the chips themselves are smaller than that socket. You need to solder each of those connections simultaneously without shorting them out to their neighbours.