At the end of Chapter 10 and the beginning of Chapter 11, we find out what the first memory that Jonas receives is. We find out that the first memory the Giver gives him is the memory of snow and the sled.
At the end of Chapter 10, the Giver tells Jonas that he will give him a memory. He tries to tell him what it will be but realizes that Jonas can't possibly understand because he doesn't know what snow is or a sled or runners or even a hill.
So at the start of Ch. 11, Jonas lies down and the Giver transmits the memory of sledding down a snowy hill.
Jonas is not expecting what will happen when he goes to see the man who is supposed to see the man who will give him the memories. The first memory that the Giver transfers to Jonas is a sensation of cold. Jonas lives in an environment where the temperatures are controlled. He feels a sensation move throughout his body and against his face. Jonas sees crystals twirling around him. He looks down and sees distance. (There are no hills in the community)
Jonas next finds himself on a sled going down a snowy hill. It is an exciting and exhilarating sensation as if he is really traveling at a fast pace.
Now too, he could feel cold air twirling around his body. (80)
When he opens his eyes he is still on the bed and had experienced his first memory.