North bridge and south bridge refer to the two support chips that make up the core logic chipset on a motherboard.
The function of the north bridge is to handle communication between the CPU chip itself and with the memory bus and graphics bus (PCIe x16 & x8) controllers.
The function of the south bridge is to handle communication between the north bridge and the peripheral buses (e.g. APM/ACPI (power management), PCI/PCIe x1 Bus, AC97/HDA (audio), SATA/USB/LAN ports, other devices).
Yes these chips are important. Without them the CPU is useless because it is unable to communicate with the motherboard and its attached components.
AMD was the first to integrate the functions of the north bridge chip onto the CPU die, therefore...