This one is pretty easy. The Junior WRC season will be the first contract you get to choose when you start a career. You will have a choice of a few different teams. Just choose one and start the career (depending on the team, the rallies might be different). You will have to race through 7 rallies that are 6 races each. Just make sure to come in first place through the rallies and the achievement will unlock after you finish the last race and return to the menus. If you need some help in making it easier, change the difficulty to easy in the options at the main menu and any other assists you may want such as braking, steering, etc.