Kriya yoga is a ancient meditation technique of truth, and self realization. The Indian sages discovered that revolving the life current (prana) continuously up and down in the spine by the special technique of kriya yoga, it accelerate one’s spiritual evolution and awareness. Kriya yoga involves the practices of pranayama, mudra, bandha and dharna. This is very intensive form of Rajayoga, focuses on awakening of kundalini shakti. Kundalini is a dormant spiritual potential in every human being. Kundalini has been discribed as surpent coiled two and half round, around the Mooladhara chakra.
The ultimate purpose of kriya yoga is to create awakening in the chakras to purify the nadis and finally to awakening of the kundalini shakti.
Kriya yoga means the yoga of practice, the movement of action. Unlike the very religious mystical or yogic practices which demands mental control and special instruction, in kriya yoga you do not worry about the mind. If your mind is dissipated or there are distractions in your mind, if you are not able to concentrate even for one second, it does not matter; you only have to continue with your practice of kriya yoga, even without confronting, controlling or trying to balance the mind.
You still evolve.