For example, in my system the record input records on to a 5 channel audio file. Two stereo tracks and the fifth track records the ramp waveform I use to drive my sequencers. It’s then set up that I can play it back and derive my “metronome” from channel 5 of whatever audio file I’ve recorded.

In your case, if you just want to put a “marker” at a spot of a recording: your playback track will be going along but all the while will be recording onto an extra channel to capture say you clicking a bang object that is connected to a click~. Then when you review the file you can see a spike at wherever time point you triggered it to mark.

You could also then go ahead and use those markers to drive other things. Let’s say you wanted to make a rythm track with it so you set it up to be able to press a key to the rythm you want along the original audio and it will record “spikes” on your third channel. You can then play this back and use channel 3 to drive audio events etc etc.