This is the heart to what your phone does so be careful when you do this if you're doubtful about something dont hesitate to ask me in the thread.. the base config is usually present in the kernel_source/mediatek/config/devicename/autoconfig/kconfig/platform. this is your base config which you will use and build with different requirments(Example:SELinux). You can always build a config from the start, I advice you dont do that until you have compiled a few kernels before. for using existing config as a base