One of the most detailed introductions on How To Meditate is a classic by Henepola Gunaratana, the monk from Sri Lanka who spent years as a Buddhist Monk and teacher. His book is Mindfulness in Plain English. The title is about mindfulness, but the book is an introduction, albeit a lengthy one, into the topic of meditation
If you want a much simpler book focused entirely on HOW TO MEDITATE, this one is easy to understand (4.4/5 Rating and 250 reviewers at Amazon)
We have had many good reviews and comments over the years on the content of this book. It has sold over 80,000 copies both at Amazon and on our websites.