This achievement is pretty self-explanatory - you need to win 50 races in any of these game types to unlock it. Just put the difficulty to ‘Rookie’ and pick one of the better teams.
Firstly you should start a championship and try to win. If you do win the championship you will unlock Championship. Next you should set the opponents difficulty level Realistic and then start another championship and win, In doing so you will unlock The true SBK™ hero achievement.
By this time you will have accumulated a number of wins but not enough for this achievement. Now you should pick your best race track and set the difficulty to Rookie and one lap, then keep going until the achievement unlocks.