Verification of all steps needed to extract MFCCs from raw audio data
Point 7: Multiply and add the FFT with the MelFilter Banks. Therefore, if you are using 26 Filter banks , we will end up getting 26 dimensional vector at the end.
Point 9: Take the DCT of the 26 dimensional vector.
Point 10: Keep the first 12 coefficients and discard the rest.

I understood MFCC features by reading this link: http://practicalcryptography.com/miscellaneous/machine-learning/guide-mel-frequency-cepstral-coefficients-mfccs/

It is very simple to understand from the link above.