Question on the 8 pins from PS on MB

[bcmind]

What does that 8 pins connecter (from power supply) do on the motherboard? the motherboard have a power supply input already... so why need that connector? i'm confused!!!

Also, what are those little Cylindrical-shape-like with 12v-print on it does (it's all over the MB)? what are they call?

Please, please let me know...