Foreshadowing is a hint the author drops about what is going to happen later. It creates suspense, which is a feeling of excitement that makes the reader want to keep reading. So foreshadowing and suspense are very closely related.
One example of foreshadowing occurs on the very first page, when Jonas remembers a plane that flies over the community.
Frightened was the way he had felt a year ago when an unidentified aircraft had overflown the community twice. (p. 1)
This foreshadows the search planes that will look for Jonas later, but it also establishes a mood of impending doom and suspense. We wonder what is going on in this community that a plane flying overhead would cause such fear.
The plane also brings in the concept of release, which foreshadows the trouble Jonas has trying to save Gabriel.
There were only two occasions of release which were not punishment. Release of the elderly, which was a time of celebration for a life well and fully lived; and release of a newchild, which always brought a sense of what-could-we-have-done. (p. 7-8)
This again foreshadows the controlling nature of the community and creates suspense over what release is.
Finally, another key element of foreshadowing is the changing apple.
But suddenly Jonas had noticed, following the path of the apple through the air with his eyes, that the piece of fruit had—well, this was the part that he couldn't adequately understand—the apple had changed. (p. 24)
Jonas sees the apple’s color, in a world where no one has color. This foreshadows Jonas’s ability to See Beyond, which means he has a capacity to be a Receiver of Memory. This also creates suspense because we are not sure what is going on.
Lowry, Lois (1993-04-26). The Giver (Newbery Medal Book). Houghton Mifflin Harcourt. Kindle Edition.