I recently bought 1/2 inch unfinished tongue and groove engineered french oak hardwood flooring. I probably should have ordered finished wood but I wasn't able to get it re-ordered in time. My question is this: Once my floor is installed how do I go about putting a clear coat of varnish on it for sealing and waterproofing? I'm mainly concerned about the complexity of the sanding process. Is it like a refinishing job that needs a professional? Do I need to rent big heavy equipment for this or is it just a matter of roughing it up a little and vacuuming the dust?

The last thing at the floor manufacturing company is adding the finish. You most likely have a floor that was sanded already. The reason to sand the floor after installation is to remove the over wood. Your flooring might have a micro-bevel that eliminates over wood that a square-edge unfinished floor comes with.
If you would like to smooth the surface a little more to remove pencil marks or smudges from installation use a random orbit sander with 100 grit or 120 grit. If you know how to use a 15 or 16 inch floor polisher you can rent one and use 100 grit screens and a thin white pad to drive the screen. A scraper will make quick work of a dent, then use a 5 inch random orbit palm sander to smooth any scraper marks.
Vacuum and apply the first coat. Use the random orbit, palm sander or buffer using the used screen, 100 grit, to cut down the grain raise that has puffed up any fuzz left from the sanding after absorbing the finish from the the first coat of finish after the floor is dry... Then, just a light abrasion between coats of finish will result in a smooth floor.