roof rack for 1996

I have a 1996 ford windstar that did not come with a roof rack. I bought a roof rack from a salvage place. can anyone tell me what I have to do to securely install this on my van. It could really come in handy. I just want to make sure I can safely install the roof rack. I will be transporting my son's small boat 3' x 7'. Anybody who can give me information on the proper way to go about installing this would be very much appreciated.