(a) Saucha.  It means cleanliness.   Most people would interpret this as cleanliness of body and surroundings.   It actually means purity of the mind or the inner self.   A yogi may appear unclean to the eye, he will emit the most pleasant aroma and most pleasant speech.  

(b) Santosha.  Means plain contentment.  Contentment shows lack of desire, which is essential to conquer the mind.    Contentment is not easily attained.   Desire is the primary cause of suffering and contentment counters all desires.  Contentment should not be misunderstood as an excuse for not performance of bounden duties.   All duties have to be performed in earnest. 

        (c) Tapas.  Means to purify ones inner self by performance of austerities.   It involves change in the outlook and attitude.   There is a greater awareness, the higher self-gets operational, old habits are burnt up, a transformation gradually takes place.   Tapa involves meditation for a long time and other spiritual disciplines as prescribed by the Guru.

         (d) Svadhaya. Reflection and contemplation on eternal truths and understanding them is Svadhaya.   It also involves study of scriptures and self-study.   This also means meditation, as this is a process of purification.