Salva is crying because he does not know what to do since the group that he was traveling with left him because he is a child. Salva was dependent on his group, but now that they are gone he has to be independent. So then he finds an old lady at her barn.
Salva's Uncle died because of the Nuer tribe. Beneath his sadness he felt stronger. When Uncle wasn't there anymore his group treated him like he was weak and useless. He will prove them wrong!
Salva is a leader because he crossed the river even when there were crocodiles in there that shows his is developing into a leader. Another way is when he lead the lost boys to Kanya. Salva is a leader by doing those things.