The sled experience makes Jonas feel exhilarated. It also shows him how different he now is from everyone else.
The first memory the Jonas receives is an important one. There is no snow in the community, because they have climate control. The presence of snow in the memory gives Jonas a glimpse into the world that was, and helps him understand exactly what a memory is.
No voice made an explanation. The experience explained itself to him. (chapter 11, p. 81)
This is when Jonas understands how the memories work for the first time. He learns how the process works, and ideas and new words just magically pop into his head.
Comprehending all of those things as he sped downward, he was free to enjoy the breathless glee that overwhelmed him: the speed, the clear cold air, the total silence, the feeling of balance and excitement and peace. (chapter 11, p. 82)
The sled memory is also the first time Jonas realizes how disconnected he has become from others due to his experiences.
How could you describe a sled without describing a hill and snow; and how could you describe a hill and snow to someone who had never felt height or wind or that feathery, magical cold? (chapter 12, p. 89)
Jonas has entered a whole new world, and there is no turning back. He will never be the same.
At first, Jonas is startled when the Giver shares the distant memory of snow. But after the experience of sledding, Jonas becomes excited, and he delights in the sensation of frigid air, going downhill over the snow, and feeling snowflakes on his face.
For the first time in his life, Jonas feels what it is like to be cold, a sensation that oddly fills him with energy. Then, Jonas feels "dots of cold" on his cheek, and he sticks his tongue out to taste the snowflakes, as many a child across the ages has done. When he rides on a sled, "the experience explained itself to him," and he does not want the exhilarating ride to end.
After the experiences of cold and sledding, Jonas feels warmth on his face from "far above." He is told that the sensation is sunshine. This sensation is one that Jonas also finds pleasurable. Jonas asks the Giver about the new things he has felt and why they no longer exist.