You provide the mixed version of your song as a stereo 24 bit or 32 bit float WAV or AIFF file and get:
Mastered version as a 16 bit 44.1 kHz WAV file
Mastered version as a 24 bit Apple Digital Masters (aka Mastered for iTunes) WAV file at native sample rate of the mixed file
Mastered version as an mp3 file for reference
DDP for CD manufacturing