Capitals and accent marks indicate the octaves. The first letter of a tuning name is usually the bass string, then the Middle Drone, lastly the Melody string(s). CGG/CGc and DAA/DAd are the most common tunings.
C D E F G A B c d e f g a b
The Bass string is usually C or D. The Middle Drone is then G or A. If you are tuning to CGG or DAA, the melody string(s) ae the same as the Middle Drone. If you are tuning CGc or DAd, the Melody string(s) are an octave higher in pitch -- as indicated by the lower case letters c or d. If you refer to the line of letters above, and count 8 letters to the right of C or D, you will find c or d.
The system goes both higher and lower than shown here, with accent marks indicating other octaves.