... I have a body which is adversely affected when I feel pain, which has need of food or drink when I experience the feelings of hunger and thirst, and so on... Nature also teaches me by these sensations of pain, hunger, thirst, etc., that I am not only lodged in my body as a pilot in a vessel, but that I am very closely united to it, and so to speak so intermingled with it that I seem to compose with it one whole. For if that were not the case, when my body is hurt, I, who am merely a thinking thing, should not feel pain, for I should perceive this wound by the understanding only, just as the sailor perceives by sight when something is damaged in his vessel... For all these sensations of hunger, thirst, pain, etc are in truth none other than certain confused modes of thought which are produced by the union and apparent intermingling of mind and body.
Page 1-29 of 1911 edition of The Philosophical Works of Descartes (Cambridge. University Press), translated by Elizabeth S. Haldane
Best commentary I have found is SparkNote on Meditations on First Philosophy:
Overall Analysis and Themes
First Meditation: skeptical doubts
Second Meditation, Part 1: cogito ergo sum and sum res cogitans
Second Meditation, Part 2: the wax argument
Third Meditation, Part 1: clear and distinct perceptions and Descartes' theory of ideas
Third Meditation, Part 2: Descartes' theory of ideas (cont.)
Third Meditation, part 3: the existence of God and the Cartesian Circle
Fourth Meditation, Part 1: God is no deceiver
Fourth Meditation, Part 2: Will, intellect, and the possibility of error
Fifth Meditation: "The essence of material things, and the existence of God considered a second time"
Sixth Meditation, Part 1: Cartesian body
Sixth Meditation, Part 2: Mind-body dualism
Sixth Meditation, Part 3: Primary and secondary qualities
Another promising guide is A Beginner's Guide to Descartes's "Meditations" (2007) by Gareth Southwell, who illustrates his own work.