How do you hook up wireless routers?

I just picked up a "wireless router". A Westell Versa Link Model 327W. It has the antenna on the back of it, but no other antennas to put into my computers. I was hoping to hook up a computer in my garage (about 50' away) and use this wireless router in the house for the computers inside as well. Am I missing something? Is there something else I need to get for my computers to make them wireless? The people at the store were NOT helpful in any way. I thought I was computer "illiterate". Any help would be appreciated.