Kriya is a direct action. It is a technique to give a sence of physical tension so that it starts to activate points in the subtle body.
Different kriyas create different tensions and as a result they have an effect on the chakras or the petals of the chakras.
Here at Satya Loka we use Kriyas from the traditional practices of the Hatha Yoga system that we teach on the regular teacher trainings.
A more advanced and complete Kriya system is taught in Sharabh Yoga, a training that awakens the energy of the petals and chakras so that you can teach Tantra Yoga as a transmission from your own energy.