Possible Duplicate:
Building a simple mp3 music player
I want to create simplest mp3 player in C or C++.
What function or API do I have to use ?
If you just want to write a C or C++ program which plays an mp3 file, you might want to look here: How to play MP3 files in C?.
If you are looking to write something more complex (say a full GUI application to select and play mp3s, including elements to play/pause, jump to a part of the song (and see what part is playing), and view song metadata, etc) than the best advice I can give you is to jump right into your program and start coding. The number of things that would need to be covered to give you an adequate response to a general question are very vast, and we don't know anything about what you are trying to do, what your experience is, or what you might have problems with.
If you jump into it and then ask questions if you get stuck on a part of it, it will overall be a lot more helpful for everyone.