Can these two words interchange each other? If not, what's the right usage?
No, they are completely different. "General" is a commonly used word; "generic" is rare.
"General" has a lot of different meanings, but as an adjective it means "wide," "covering everything," "including everything."
"The old-time general store sold everything--food, clothing, and hardware."
"In general, the United States has a temperate climate, but there are many exceptions."
"Massachusetts General Hospital treats everything; the Dana-Farber Cancer Institute specializes in oncology."
"Generic" means "the plainest and most ordinary of its kind." Often, it means "lacking a brand name."
"Don't pay extra for brand-name aspirin; aspirin is aspirin; just buy the cheapest generic aspirin."


