The central idea is the same as the main idea. Most of the time, the main idea is mentioned in the Title. Without reading the essay, I do not know what the central/main idea is.
Hema’s mother has a powerful connection to her Bengali culture, and she also has the culture of being a mother. She talks to Kaushik in Bengali language, yet also she also has the sympathy and care of a mother for her child, which is common in all cultures. Kaushik has a mix of American and Bengali culture, that’s why she understands Hema’s mother when she talks to him in Bengali, even though he replies in English. As Kaushik went to the market, he brought back broth and magazines which is quite popular in American culture. The passage shows how Jhumpa’s life is a mix of cultures that integrates with one another. She has Indian culture but was raised in American culture, and that entwines with the culture of her ancestors.
A suffix is a bit of speech that gets attached at the end of a word to modify it or to make it into a related word. For example, you can attach -er to the end of a great many verbs to get a word meaning "person who does X"
