What are the main differences between front wheel drive, rear wheel drive and four wheel drive cars?

In front wheel drive,power reaches only on front two wheels,the remaining two rear wheels rotate due to rotation of front two wheels.rear wheels are not connecte with engine. same thing happens in rear wheel drive,power is reached on rear wheels only.front wheels rotate automatically on the result of rotation of rear wheels. four wheel drive means power coming out from engine are provided on the all the four wheels at the same time unlike front and rear wheel drive(you can say it as atwo wheel drive).All the SUVs are four wheel drive. they consume more fuel,give less efficiency.

For a good AWD, the fuel consumption is imperceptibly worse.  You'll never notice.  Many AWD are biased in one direction or another.  The Subaru automatic was (may be still) almost pure FWD, when not slipping.  This would make it nearly impossible to tell AWD from FWD in regular driving, and fuel economy.  Others bias towards the back (the 911).  The Subaru manual and Skyline AWD don't bias towards either and simply deliver more power to the slipping wheel(s).  Whether they do so through strategic use of brakes, or locking slipping transfer cases is something almost nobody would be able to tell by driving it. If you want to find out, pull into sand, or mud.  Floor it.  See which wheels throw up mud/sand.  Not much more can be done driving it, unless you can drive closer to the limits of the car than I'd assume from someone who would ask such a question.