Ground effect is a phenomena that occurs when a plane of any size descends to within approximately a wingspan above the ground. So a 747 will enter ground effect before a J-3 Cub will. When the plane's in ground effect, it's more effecient. This is due to the lessening of "Wingtip Vortices."
Wingtip vortices are what cause "Wake Turbulence." Like wake from a boat in the water, the air behind the wingtips of a plane gets disrupted and turbulent. Air flows over a wing the same until you look towards the tip, when it's different. I can't really explain why it's different, but it is. And if you were to look at a wind tunnel that can show the flow of air over a wing, you'd see that, behind the tips, it's like a cyclone moving backwards and parallel to the body of the plane. It's like tipping a tornado on it's side. This cyclone effect happens as long as air is moving over the wing. As the wing (plane) comes in to land, for example, the cyclone itself is disrupted by the ground. Where the vortex would normally spin back and down from the wingtip, it's now hitting pavement. So it's reducing the entire thing. That means less drag, since vortices create drag.
Flaring is what planes do when they are in the last stages of flying down the approach. It's what you see after the expressway turn to 31 is complete, they're past your dock, and over the threshold. The nose comes up even farther and the main gear is about to touch. That maneuver is called the flare.
A "floated" landing is the opposite of a quick, abrupt touchdown. In a floated landing, the plane probably came in too fast. If you have flight sim on your PC
, try flying down to the runway in a 172 at 130kts. Cut the power, and the plane won't want to land, because it's going way too fast. So a floated landing is basically a prolonged touchdown. This is bad on a short runway for obvious reasons. In fact, planes decelerate about 3 times faster on the ground than they do floating down the runway (I forget what plane was used in that example I read somewhere, but it's the same idea for any plane).
When the reduced wingtip vortices take away drag, the plane is flying more effeciently. Remember, thrust has to overcome drag for the plane to accelerate. When thrust is low on landing, any reduction in drag will make a difference. Less drag will keep the plane in the air longer, causing it to "float" down the runway.
Back to wingtip vortices, the winglet reduces them. So you can see how all this comes together. The less drag, the faster a plane can go, or if it flies the same speed, it can fly at it with less thrust because the winglet has taken away that little bit of drag that trailed from the wingtip.
I assume raked wingtips are designed to do the same thing, although I am not certain. But reducing drag and thus reducing fuel burn as well has got to be one of their primary reasons for being put on the end of a wing.
Hopefully this answered your questions.