To take your points in order,
1. It will allow you to share an Internet connection sharing between two computers, as long as both have wireless networking. A lot of new laptops, and all centrino laptops have wireless already built in.
2. By itself the wireless USB adapter does not allow Internet connection sharing. (See above).
3. The adapters are used to setup a wireless network between computers.
4. You have sort of been misled, also see above.
5. See 3.
Does you laptop have wireless built in? if so you should be able to network the two computers and setup Internet connection sharing. (this is probably a new thread, and probably best posted in the networking forum.)
If your laptop does not already have wireless you will need another wireless card, either PCI (to fit in the small slot on the side of the laptop) or USB (same as you already have)