Instructions
Click on the career tab in the bottom right portion of the screen. The career tab has an icon of a man seated at a desk. This tab will show you what your job is, how much you get paid, how well you are performing at the job and when you work.
Note the time and days of the week that you work in the career tab, and ensure that your Sim is well-rested, dressed and fed before that time.
Click on the carpool icon when it shows up in the top left corner of the screen shortly before you are due at work. You should also hear a "beep beep" from the car letting you know it has arrived. The Sim will walk out to the waiting car and go off to work.