how to do clustering of MFCCs?

i was trying MFCC code from one website in which following parameters are defined.

 % Define variables
    Tw = 25;                % analysis frame duration (ms)
    Ts = 10;                % analysis frame shift (ms)
    alpha = 0.97;           % preemphasis coefficient
    M = 20;                 % number of filterbank channels 
    C = 12;                 % number of cepstral coefficients
    L = 22;                 % cepstral sine lifter parameter
    LF = 300;               % lower frequency limit (Hz)
    HF = 3700;              % upper frequency limit (Hz)
    wav_file = 'P0021.wav';  % input audio filename
its giving output as MFCCs--<13x3498 double>. what is that value 12=C? what are these so many output coefficients? how to get few coefficients?how to represent them as cluster?please help me.