This verse is from the Bhagavad Gita, Chapter 6, Verse 20. It is written in Sanskrit and translates to English as follows:
yatroparamate chittaṁ niruddhaṁ yoga-sevayā
yatra chaivātmanātmānaṁ paśhyann ātmani tuṣhyati || 20 ||
"Where the mind becomes calm and controlled through yoga practice, where the practitioner sees the soul in the soul itself and is satisfied in it."
In this verse, Lord Krishna explains that when a person practices yoga, his mind becomes calm and controlled. In that state, the practitioner sees his soul and is completely satisfied in the soul itself. This is the description of the highest state of yoga, where after self-realization, a person goes beyond external happiness and sorrow and experiences complete peace and satisfaction in the soul.
This shloka describes the state of yoga which is called 'samadhi' or self-realization. This state is the ultimate goal of every sadhak in which he completely controls his mind and senses. The main purpose of yoga is that the sadhak can calm his mind in such a way that he can experience the soul and is not completely distracted by the outside world.
yatra - where
uparamate - becomes calm, rests
chittam - mind
niruddam - controlled, restrained
yoga-sevaya - by the practice of Yoga, by the practice of Yoga
chaiva - even more
atmana - by the soul
atmanam - the soul
pashyan - seeing, experiencing
atmani - in the soul
tusyati - is satisfied, rejoices in the inner joy.