well, you gotta get a wireless card or router that can have an external aerial attached

you then gotta get some nice expensive cable to run from there to your external aerial

you stick the aerial on your roof (or where ever others can get LOS ("line-of-sight"))

thats about it.

http://shop.borg.co.nz sells almost everything you will need

if you want to make your signal as strong as possible, the idea is to have the least distance between your wireless card / router and the external aerial, so some people stick their PCs in their roof or pull apart their wireless router and put it in a weatherproof box and stick that up on the roof (and do what is called POE ("Power Over Ethernet")) alongside their aerial.

good luck