Therefore, you will first see this message:
What will happen next, assuming you choose Yes is the song will start and you will see the following display:
There are three lines. The bottom line is the important one. It is the cue line.
When you reach the point in the song where this line is to be displayed on the music player - click the window. Anywhere.
The contents of the cue line will move to the centre of the display - highlighted and in black. This is the current line.
Whatever was in the current line beforehand will have been moved to the top line, the previous line.
As you can see, I am working through the Evanescence song "My Last Breath". We have already heard the line "Hold on to me, love" and am now listening to "You know I can't" and I am waiting for the part "stay long" at which point I'll click it to mark the time position.
If you need to abort matching before the song has finished, just close the window. All of your matched-up timings up until that point will be visible in the editor.
The caveat, though, is if you begin matching up again, you must begin again from the beginning.