You use interior to describe something that is inside a building or vehicle.
The interior walls were painted green.
内墙被漆成了绿色。
An interior minister, ministry, or department in some countries deals with affairs within that country, such as law and order.
The French Interior Minister has intervened in a scandal over the role of a secret police force.
法国内务部长对一起有关秘密警察部队职责的丑闻进行了干预。
interiors
The interior of a country or continent is the central area of it.
The Yangtze River would give access to much of China's interior.
长江使得人们能够到达中国内陆许多地方。