WIM Fiona Steil-Antoni explains even more tactics you need to know!
Surprise your opponents with powerful winning moves
Pins and skewers are two ways that the "long-range" pieces (the bishop, the rook, and the queen) can attack two or more pieces simultaneously along the same rank, file, or diagonal. This is another basic tactical tool that is easy to understand and critical to master.
"Introduction to Tactics" introduces the student to the tactical tools of chess (forks, pins, etc.).
Silman Teaches Tactics - IM Jeremy Silman The classic challenges in this module contain combinations and tactical material for intermediate and expert level players (USCF or Elo ratings between 1400 and 2000+). Some challenges here are difficult even for masters and above. However, players of all levels can enjoy and learn from these examples.
"Intermediate Tactics" presents tactical exercises that are significantly more difficult than those seen up to this point.
"Step Up in Tactics" presents exercises, both checkmates and tactical, which are somewhat more difficult than the material covered so far.