It tells me where blunders and mistakes are made
It does not show me what the blunder or mistake was
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[it] then gives you a possible line of best play
It does not show me . . . how to capitalize on [the blunder].
I see you're confused about something, but I'm not sure what it is.
Sometimes mistakes are positional in nature. The engine is criticizing your move because, for example, your pieces are much less active vs the opponent's pieces. In the long term this will lead to material loss.
I suggest you download the free Lucas Chess (http://www-lucaschess.rhcloud.com/index.html), save you chess.com game as a pgn, then read it into Lucas Chess and analyze with Stockfish 8 set to 12 ply or higher (I generally use 20 ply - about 70 seconds/half move on my computer).
You get recommended lines at every half move and it becomes clear if your "blunder" is a bad move or of Stockfish (on Lucas Chess or on chess;com) simply found a what it thinks is a much better move.
It also occasionally comes up with some sacrifices of Knight for 3 Pawns combinations you might overlook and aren't spelled out on chess.com's analysis.
I've been using the computer analysis tool to look at games I've played. It tells me where blunders and mistakes are made and then gives you a possible line of best play instead. It does not show me what the blunder or mistake was or how to capitalize on it. I need to see how to identify the blunders of myself and my opponent and capitalize on them. I also have chess master 10th anniversary edition.