The "chipset" often connects the CPU to RAM, PCI, AGP slots and may have the IDE and other interfaces in those chipsets.
The differences are subtle and revolve around memory support and speeds.
Beyond that, you will research such in motherboard reviews or reading intel.com developer guides and more.
Hint: This space is too small to dive too deeply.
What's with all the different types on chipsets on mobos? like 875, 915, SiS661FX?
It confuses me, I usually get 875 chipsets, but I was just wondering whats the big difference between them.