Andon Rangelov 
Fork, Pin and Skewer Tactics in One Move [EPUB ebook] 
Chess Exercises for Kids

In chess, a tactic is a series of moves that limit the opponent’s choices while potentially gaining actual advantage. Fork, pin, and skewer are three basic tactics in chess, and we provide 100 exercises in this book to practice them. The book is appropriate for children and novices.
Please keep in mind that these are do-it-yourself exercises, therefore you must be familiar with all of the basic chess principles. Use “look inside” for additional details.
If you attack two of the opponent’s pieces at the same time by using one piece, this is called a fork.
When a defensive piece is stuck in a pin, it can’t move without exposing a more valuable defending piece on the opposite side to assault.
A skewer is an attack upon two pieces in a line and is similar to a pin.