
In terms of actual practice, meditation is described as sitting comfortably and just feeling your breath, when your attention wanders from it, forgive yourself and just return to focusing on the breath. It's about being in the present moment, not letting yourself be consumed by thoughts of the past or future, and viewing things with a remove, simply observing things as they are rather than having a huge emotional response to them.
Harris also writes in the book about attending a ten-day silent retreat in Marin County led by Joseph Goldstein. The first five days were difficult for him, and then after being encouraged to not struggle, or worry about the struggle so much, he had a breakthrough of sorts, not necessarily enlightenment, but something where he could see the benefit of being there. Several of the things that he noted as having taken from the retreat and speakers there were to ask "is this useful?" about a potential reaction of his to an problem or stressful situation and to respond to said difficult situation with the steps of (A) recognize it, (B) allow yourself to lean into it, (C) investigate your reaction to it, and (D) have a non-identification or non-emotional response to it. Additionally, Harris noted having learned from the retreat the practice of metta meditation, the directing positive thoughts towards another person, for instance with thinking about them and mentally wishing "may you be happy, may you be safe, may you be healthy, may you live with ease" towards the person.
Towards the end of the book Harris writes more about others and the notion of having positive interactions with people and acknowledging their humanity, through things as simple as having a practice of making eye contact and smiling towards those he passes. Also noted is the idea of keeping in mind the question of "what matters most?" when considering a response to situations.
The book had a lot of interesting material and the writing of Mark Epstein seems a good place to go for someone wanting to learn more about meditation.