2) FireWire is also known as IE1394 on many computers. (Same device... just a brand-name thing)
IEEE 1394, not IE.
IEEE 1394 is the interface standard. Technically there are several versions of it; Firewire 400 or IEEE 1394-1995, IEEE 1394a-2000 (the standard utilized by most cameras), Firewire 800 or IEEE 1394b-2002, Firewire S1600 & S3200, Firewire S800T or IEEE 1394c-2006.
Firewire is the Apple name for the interface, and since Apple developed it it has become the common name. Sony refers to IEEE 1394 as i.Link, and Texas Instruments refers to it as Lynx.
The 4 pin connection is the same as the 6 pin, only a much smaller size and it does not include power as the 6pin connection does. Typically desktop computers will have the 6pin connection, laptops can have either, but usually will have the 4 pin, and cameras almost always will have a 4 pin. The smaller 4 pin connector is part of the IEEE 1394a standard.
The protocol most cameras will use to actually transfer digital video over the IEEE 1394 connection is the DV protocol.
There is a whole lot of additional information on both of these topics, IEEE 1394/Firewire/i.Link/Lynx and the DV protocol...
As Zen said, your question isn't very clear.
What specifically are you confused about, and what would you like to know?