Decoding Full Rate GSM Encoded File

I have 2 files first is Full Rate GSM Encoded and second is ADPCM Encoded, i have opened both files successfully with audacity(using external library ffmpeg). Now i want to know that can i use Audacity builts that are available on (size 230MB) to make my own small decoder? If yes then please do provide me some help so that i can begin this thing. Kindly explain in simple words as i am a beginner.

Both lame and ffmpeg are stand-alone programs as well as modules/plugins. I don’t think you need Audacity at all.

As Koz wrote, FFMpeg is available as a standalone application and as a library for use in other programs so Audacity does not really come into this.
The FFMpeg documentation is here: