Complete any three street races to unlock. You do not have to win, just complete the race. I suggest you pick any car you like to drive and that handles well because the other cars will be tuned to match you, so it make little difference which one you pick from an advantage standpoint. Also suggest a couple of the shorter races around Yarra Valley, as some of the street races are fairly long. It is OK to pick one street race you prefer and run it three times.
Pick any street race or any midnight battle. Anything that is not a specifically identified as a street race or midnight battle will not work, nor will any will any rivals races.