This site has two parts.
1. The first part is a book that explains chess tactics (in other words, how to make winning moves). It assumes no prior knowledge of the subject. Everything is explained progressively and in plain English. You can read it by clicking anyplace in the table of contents below. The headings can be expanded one at a time by clicking on the [+] signs, or click here to expand all of them at once. (And then you can click here to collapse them all at once.) There are 20 chapters, about 200 topics within them, and over 1,000 positions discussed.
2. The second part is a trainer: a set of puzzles shown without solutions that you can use to practice. Click here or on the "Chess Quizzer" box to the left to use it. You can try a random position from the book or one that involves a particular topic. The trainer allows you to ask for a hint if you're stuck, and to see the answer when you are done.
You can always come back here by clicking the "contents" button in the upper right corner of every page. If you arrived by a different route, the best address for returning is www.chesstactics.org. This whole site has now been made much friendlier for mobile devices thanks to the help of a kind and ingenious reader.
Book versions of this site are available: over 700 pages in total in a two-volume set. Here are links to book one and book two. Check out other books by the author about language here, metaphor here, and law here and here.