What is Yoga?

It is often noted that the word yoga comes from the Sanskrit root yuj, meaning, in the sense relevant here: "to join, link, connect," "to prepare, make ready," "to use or engage," "to meditate on and unite with God."
Thus, without significant semantic stretching, we can say that yoga - both in the Sanskrit dictionary and in Bhagavad-gita - primarily refers to a spiritual practice in which one readies the soul to unite with God.
A Comprehensive Guide to Bhagavad-gita with Literal Translation, page64
H.D. Goswami
If it's more than just exercising, how can yoga be practiced in our daily lives? What disciplines are involved? Bhagavad-gita teaches how one can learn to incorporate yogic principles in one's life and achieve higher levels of consciousness.