The Kan Variation is a common line in the Sicilian Defense and starts with the moves:
The Sicilian Defense is widely known as one of the most solid defenses against white. The Kan Variation rushes to play a6 and stop white from advancing Nb5. This is a common themes in many Sicilian Variation, like the Najdorf Defense, but the Kan Variation plays a6 as early as turn 4.
This opening allows black to be very flexible based on where white moves. White can continue normal development with 5. Nc3 or Bd3 to prepare for a king side castle.
The critical square for black to control early in the game is e5. Black does not what white to start pushing the pawn on e4 to e5. This is usually done by bringing the queen to c7 (defending e5) and the knight to c6 (defending e5). These are normally development moves but are important to start with before black tries to develop other pieces like the king side bishop and knight.
If you would like to learn more about this variation be sure to watch the video below.