This site has two parts: a book that teaches chess, and a quizzer that lets you practice on problems with the solutions hidden until you want them. To briefly elaborate:
1. The first part explains chess tactics: how to make winning moves that capture the other player's pieces or that lead to checkmate. 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. 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're 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.
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. You can check out other books by the author about language here, metaphor here, and law here and here.