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.