In plain words
We must not knowingly commit any acts of violence. A person who keeps complete Ahiṃsā is not to be found anywhere in this world. Unknowingly, we commit many acts of violence. But knowingly, at least, with our conscience as witness, we must not stoop to any violence at all. Of violence done unknowingly we may say, ‘This is a mistake’, but we cannot call it sin. Only the wrongs done knowingly come to be called sins. So yama has taken the vow of Ahiṃsā as its chief step. Next, speaking Satya, and through it gaining mastery of Manas. By nigraha man can win anugraha. Besides this, love for all living beings is a chief principle in it. A person must always pass his time in happiness. He must not let any sorrow, any grief or any unrest arise within himself. Having such good qualities, keeping brahmacarya through control of the senses, recognising the divine principle, and growing in detachment from desires and attachment to God: that is yama.
Gaining purity within and without is the chief point in niyama
The second is niyama. That is, niyama is nothing other than the dawning of attachment to the Supreme Principle. In this niyama, purity within and without is most necessary. As we clean the body with water, in just the same way we must purify Manas with Satya. We must purify the Buddhi with Jñāna. We must purify the prāṇa with learning and tapas. This does not call for great effort. In the daily rites a man performs every day, purity of body is most necessary. This purity of the body is a practice carried out for the sake of health and the sake of joy. But merely by purifying the body we do not gain Ānanda. The chief point here is to purify Manas. This Manas is thickly covered by impurities such as attachment, hatred, envy, Ahaṅkāra and ostentation. If we want to cleanse such impurities: purifying Manas with pure and sacred feelings such as the feeling of Satya, the word of Satya and good resolve.