Look on the roof, are there any mounting points? Perhaps with rubber or plastic covers? Usually its just a simple bolt on affair. Sometimes you need to take off headliner inside and go from there. If you get the roof rack from a dealership (assuming its a honda part your buying, not aftermarket) they can and will provide instructions. If they refuse to help you, kick em in the nuts and ask again.
Like chris said, most liekly there are videos out there, but it really is fairly straightforward.