Do I need to write programme for multiwii nanowii?

Its probably a dumb question but I was just curious. I received my multiwii nanowii module today and I was going through some multiwii codes. I found out the multiwiiconfig.h code and the gui for that. And apparantly it gives you pitch, roll and yaw and everything that you need.

Now my question is; if you just use that piece of code, is there any need to write a seperate code for simple balancing? Like I just want to achieve some simple quad-copter balancing. So do I need to create some PID code for that? or if I just use the multiwiiconfig.h, I can achieve the stabilty?

The example codes are just that, examples. They show you what it can do and that is it. If you want it to stabilize your copter you'll need to find or write code that can do that. Your code will need to pole the gyro and based on the readings from the gyro send commands to the copter to make the needed adjustments. Start looking at what others have done with the device and see what code they are using.