Tailing? questions.

[ɃƵ I got your back brother]

What exactly am I tailing? They seem to be doing stuff but I can never figure out what, it says they are a fixer. They never seem to just drive off so I assume they don't know im tailing them.

After you finish a tailing mission do they KNOW they were being tailed, and lost?

[Nightarix]

assuming you're referring to the "Online tailing" missions, it's other players, their awareness depends entirely on if they check one of the various "tricks" for testing if another player is in their sessions(there's probably a guide in the multiplayer sub-section that details all of them) and far as i know tailing doesn't show a score screen to the tailed, just the tailer.