What is the main conflict in "The Giver"? What is the problem Jonas has to solve?
The main conflict is when Jonas is assigned in the Community as the Receiver of Memories.
Since the main conflict is what Jonas is assigned, the effect of that is that it causes him to question the society he lives in and its restrictions set upon the Community by the Elders.
The problem Jonas has to solve is the way the Community runs. The Elders set many restrictions upon the Community and they have lived so long like that, that they know no other way to live. But because Jonas is receiving such vivid images, he wants the rest of the Community to feel as he is.
But, as a Receiver of Memories, he is not allowed to share what he sees. That causes him to break several rules and eventually run away.