How to use API to read and write configuration files ( the suffix name for ini )

The .NET Framework doesn't contain any classes for reading and writing .INI files. The view nowadays is that you should use XML configuration files instead.

However, there are several articles on Code Project about dealing with .INI files.

This old article is the simplest and, arguably, the best:

http://www.codeproject.com/Articles/1966/An-INI-file-handling-class-using-C