One particularly profound moment in the novel that deals with Ralph learning to be brave is when he and the hunters travel through the forest to find the beast after Samneric have spotted it on the side of the mountain in Chapter Six. They reach Castle Rock, a part of the island that none of the boys have ever visited, not even Jack, and Ralph and Jack toss back and forth who should go first to check for the beast. Jack is sure that this is where the beast must hide, since he has been all over everywhere else.
In that moment, Ralph sums up his courage, and "something deep in Ralph spoke for him, 'I'm chief. I'll go. Don't argue'" (104). Ralph proves his bravery by volunteering to go and face the beast when none of the other boys would. Golding proves Ralph's bravery through his actions and selflessness; he alone went on to face the beast despite his fears.
You might have trouble finding direct quotes or descriptions of Ralph as being brave but you will find examples of Ralph exemplifying bravery. For one, Ralph isn't afraid to assert his role as chief. He realizes that he needs to be the surrogate adult on the island. And he takes on this role because he has to, stressing the need to keep the fire going:
“And another thing. We nearly set the whole island on fire. And we waste time, rolling rocks, and making little cooking fires. Now I say this and make it a rule, because I’m chief. We won’t have a fire anywhere but on the mountain. Ever.”
Ralph takes on this role in spite of the fact that he, Piggy, and some others wish a grownup was there. At the end of Chapter 5, they take turns noting how grownups would better handle their situation. This is ironic because the grownups are at war.
At the end of the novel, when the naval officer asks who is in charge, Ralph says that he is - even though the rest of the boys had turned to Jack's side and even though saying he is in charge puts the responsibility of their fall into savagery on Ralph's shoulders. He cries at the end, not because of fear, but because of their lost innocence.