White to move. No check does anything useful, nothing is hanging, there is no fork. The winning move is 1.Qh6, which threatens nothing this move and mates the next one.
7 
2 
g Black’s g-pawn has been traded off somewhere earlier, which is the only damage in his position, and it is enough. The knight on f5 covers g7. After 1.Qh6 the queen covers it too, so 2.Qg7 is mate: the king cannot take a queen that a knight defends, f8 and h8 are covered from g7, and f7 and h7 are his own pawns.
Look at what Black has and cannot use. Two rooks. The one on a8 is stopped by its own pawn on a7 and can only slide along the eighth rank; the one on f8 is stopped by the pawn on f7 and cannot get to the g-file because the king is standing on g8. There are fourteen legal replies to 1.Qh6 and every one of them loses to 2.Qg7 mate.
A net is not a forced mate
The difference matters at the board. A forced mate is a chain of checks that you calculate move by move: this check, that reply, this check. A net is a shape. You are counting squares rather than moves, and the two questions are whether the king has anywhere to go and whether help can arrive in time.
Which is why nets are the harder of the two to find. Every club player looks at the checks first. Hardly anyone looks for the move that gives the opponent a free turn and wins anyway.
Count squares, then count helpers
Start with the king’s flight squares and cross off the ones his own men block. On g8 with pawns on f7 and h7 and a rook on f8, the king above has exactly one, h8, and the queen on h6 takes even that.
A king with all three pawns still at home on f7, g7 and h7 is safe from most things and helpless against a queen that lands on the seventh or eighth rank, which is the argument for spending a move on h6 or g6 while you have time. There is more on that under luft.
Then count attackers against defenders on the square you want. Two attackers against one defender is mate. Two against two is a pleasant idea and nothing more.
Building one over the board
Nets appear when the enemy king is short of air and you have two pieces near it. Queen and knight is the classic pair, because the knight guards the squares a queen cannot guard for herself, and the queen can walk right up next to the king knowing she is defended. Rook and bishop do the same job along a diagonal, and rook and knight do it in the corner.
Train them as mate in two puzzles rather than mate in one. A mate in two whose first move is quiet is exactly this pattern, and once you have solved fifty of them the move 1.Qh6 stops looking clever and starts looking obvious.