Satsang is "being together spiritually at a place where Reality (God) is spoken about". Sat means truth, sang means to be together. Without satsang, without learning about reality there is no way for man to change or improve himself. The glory of the satsang has many times been sung by great saints and poets.
Our spiritual development is greatly influenced by the company we keep.
From bad companions we will pick up bad habits, while connection with pure, spiritually oriented people will fortify our positive qualities. And if we are lucky enough to be in the presence of a God-realized Master, a saint, spiritual awakening will surely start in us. The extraordinary spiritual atmosphere and blessing of the satsang will recharge our spiritual energies for days or even weeks.
Once Narada, the Guru of the Devas asked the Lord Vishnu: Oh Lord, please tell me, where are you mostly? In the heaven or in the hearts of meditating yogis, or someplace else? And God answered: Neither here, nor there am I, oh Narada, but there I am where my bhaktas, in the satsang, sing my glory.
This parable, taken from the Hindu mythology shows the uncomparable value of the satsang.
At satsangs under the guidance of the Master, or by His blessing and spiritual presence, if He is physically absent, divine wisdom and self-realisation is spoken about, bhajans (spiritual hymns) are sung and explained, or holy scriptures like the Bhagavad Gita, Vedas, Upanishads or biographies of the saints are read out. At the end there is prayer and the meeting ends with a light vegetarian meal.