I would pay it to some scientists and make them build the portal gun or I would build the house from a show called future home (its a home with tons of gadgets.)
What i would do first,is buy tons of chocolate.Second,i would by a house,third,i would get a rock climbing place.then i would get technology.I would save the rest.
I would wander busy cities randomly tossing handfuls of hundred dollar bills into the air and watch people fight over 'em,,that should last a while. Good entertainment
That would actually be incredibly funny. I would save like 500 million, then use the rest for college, charity, an awesome house, cool cars, and probably go lose a million or so at the AG casino.