In "Where Have You Gone, Charming Billy?" what is the conflict?
I have had to edit your question down so that it no longer asks multiple questions according to enotes regulations, so I will focus on the conflict in this story.
The conflict is very quickly established in the first paragraph. Ostensibly, this is a story about the external conflict of the Vietnam war, and in this story we are presented with a platoon of soldiers in the "primitive stealth of warfare." However, alongside this external conflict, it is clear that there is a massive internal conflict going on within the character of Paul Berlin as he clearly wants to dream himself away from his present setting and pretend that he is not in the war and seeing things he would rather not see:
He was pretending he was not in the war, pretending he had not watched Billy Boy Watkins die of a heart attack that afternoon. He was pretending eh was a boy again, camping with his father in the midnight summer along the Des Moines River. In the dark, with his eyes pinched shut, he pretended... He pretended he was not a soldier.
Clearly, this is a story about the effects of war on one individual and how he faces this immense internal conflict to accept where he is and the kind of job that he has to do. Of course, the rest of this riveting story shows us how this conflict is played out.