The Benoni Defense is a very aggressive line that black can play to counter the very common open by white d4. While many defenses against the queen pawn opening are closed and drawish, the Benoni Defense gives black many opportunities to not only equalize the position, but also to gain an advantage and play for the win.
In the Modern Benoni Defense, the main focus of the game is white’s center control of the light squares with it’s key pawn on d5 and black’s control of the center from the dark squares. Black will usually fianchetto his bishop on the kingside to g7 to add extra support to the dark squares.
For a white player you want to keep constant pressure on the d5 square and use it later on to set up outposts for your minor pieces and to apply pressure on black. For black players you want to keep white from applying pressure and keep them from getting any outposts on the e6 and c6 squares. The Benoni Defense usually opens up after the opening which means that bishops are more powerful than knights so be cautious about trading off your bishop.
Black should get lots of counter play and should have a very good game after things open up in the middle.
Watch the video below to watch more detailed explanations of the opening, multiple variations, and extended lines.