How does Ralph assert his power in "Lord of the Flies"?
Although he at first is reluctant to accept power and to accept the symbolic conch, Ralph finally sees the conch as the way for him to explain the importance of "civilization" to the boys. He is frustrated at the lack of building that has been accomplished and the lack of proper sanitation - but it isn't until the missed rescue that Ralph finally sees that something must be done.
Ralph uses the conch to call the group together. He asserts his power by refusing to let go of the conch until he has finished speaking. He won't let anyone interrupt his speech - and won't let go of the conch as a result. Ralph, the symbol of civilization in the story, lays out his arguments in a logical and rational manner. He talks about the need for the fire and the shelters. He explains away their fears.
Unfortunately, although he is able to assert power in this way, that power evaporates with the Jack's ability to reestablish fear. Jack asserts his power through intimidation and instinct. He sees physical strength as the way to have control, and is able to bully most of the others to go along with him. In the end, Ralph's rational speech and the conch itself will be lost.