The main idea of the text is that Tanitoluwa Adewumi is a boy who overcame great obstacles to eventually become one of the best chess players in the country. Some details that support this idea are: the fact that Tani's family were refugees from Nigeria and homeless at the time he learned how to play; the fact that he learned chess less than a year before winning the 52nd New York State Scholastic Championships chess tournament; and the fact that Tani's chess rating started at 105 and is not at 1587.
These details allow you to better understand the main idea because they show what a difficult situation Tani's family faced in the United States. They also show the enormous improvement of Tani's skills. Finally, they show how special he is, and how his persistence paid off.
When talking about writing, “explicit” means something that is stated plainly, while “implicit” refers to something that is implied and not stated directly.
