The functions of chipsets are borken into two devices with one providing an interface from the CPU to the memory, AGP function and the other providing controllers for IDE, ISA, PCI and USB devices.
Bus, or other similar names such as the address bus, data bus, or local bus is a data connection between two or more devices connected to the computer. For example a bus enables a computer processor to communicate with the memory or a video card to communicate with the memory.
Memory has two basic kinds. RAM is storage on chips but temporay. Once powered off, it is gone. Kind of like a cache in which stuff you do on the computer is stored into memory for faster access. ROM is also storage on chips, but you cannot write to it. It is used to hold instructions to start up the computer. Permanent even when power is turned off. There are other types of memory, but these two you'll here the most.