At first look, white is pretty safe. All pawns are protected, and pieces are concentrated on d-f files. Black Bishop on d4 is under attack. If black Bishop retreats, white might go Knight h4 to get rid of one Bishop, and also try to attack on the King side.
Right now, white's biggest worry is the light squares: b1-f5 diagonal.
How should black strike while iron is hot?
Because the King is behind pawns, with some spaces, the first question we always ask ourselves is: can we open the King? Yes, one possible move, Qxb3. Is it working? We need sure follow-up before we plunge in.
If you remember the famous pattern: Bishop-Rook-King checkmate, then we know we are threat checkmate on b1. White will take our Queen with a2 pawn, but we will take it back with our Rook. Any defense for white? Not much. White has to move away d2 Bishop. No matter where it moves, we will do Bishop Bf3+. Our Rook will guard the d2 square (discover) and mate will follow.
Here, the worst piece for white is the Bishop on d2. It blocks the Queen, the Rook, and the King, basically cut the connection between Queen side and King side