Nirvana is the experience of profound peace of mind associated with Moksha. For the meditator it is the meditation of a lifetime! To experience this state is the desire of all meditators. There is deep silence, peace and tranquility as one floats in spacious, timeless awareness. Visually, one is immersed in a field of beautiful light. There may be delightful sounds or profound silence. The main feature is the feeling of sweet effortlessness, bliss and the thought comes "I want to be in this state forever!" Moksha is the experience of Nirvana 24 hours a day, during all phases of daily life including deep sleep, dreams, and all forms of activity - not just during meditation. Usually Nirvana arises during meditation and then over time gradually overtakes the life.
We know the instruction of Krishna in the Bhagavad Gita (Chapter 2, verse 48): Yogastah kuru karmani - established in yoga (Divine Union with Krishna as His Eternal Companion), perform action. So we begin each meditation with yogastah - we sit comfortably and turn the attention inward and find the silence that is deep within. For about half a minute we identify with that silence and know this is our connection to Krishna, this is yogastah. Then from that spacious silence we look back to the conscious thinking mind and let the conscious thinking mind start the mantra. Like turning the ignition key switch or pushing the Start button on the car, we notice the engine is running and we let go. So we let go of the mantra and watch and follow it from our yogastah perspective.
Thinking the mantra by the conscious thinking mind is Dharana and watching the mantra as the conscious thinking mind engages in the thinking process is Dhyana. Between each thought of the mantra is Samadhi - the simplest form of awareness of the mind where there is no thought, no activity, only Pure Being. The whole experience of yogastah is Nirvana.