What does "an opportunity to win a tempo" mean?
Thank you for your prompt comment.
It looks like I need to focus on learning about this.
Is there a lesson on this on chess.com?

A tempo is a move, simply put. Nd5, at least on move 9, would've attacked the queen, forcing it to move. Capturing on f3 is terrible, since if the bishop captures, you capture the queen with check, so they cannot capture your queen. You can then capture the bishop with the queen, since nothing defends it, and capturing with the pawn would needlessly open your king to g file attacks. If the queen captures, you simply recapture with the pawn and are up a queen for a knight. The queen also cannot stay on the f file, since every square is controlled. In fact, you're also threatening to capture on c7 with a fork on the king and rook, so the queen has to immediately retreat back to d8, meaning black wasted a move doing nothing after all.
When I'm doing match analysis, I can't make sense of this.
The coach pointed out that "9.Nd5" is the best.
I don't understand what it means and I'm at a loss.
Also, how should I learn about tempo?