When your Tama is four or five years old, you will get a [!] mail. When you check it, your Tama will look mad at the teacher, and will graduate. Shortly after, you will get another [!]. When you check it, you'll be at the place where you apply for a job (looks like weird buildings.) Press the A button, untill you see one you like, then use B to select it. You have to get 3 Os in order to get the job. If you get any Xs, then keep applying for the jobs untill you get accepted.
Once you get accepted, you need to go to the ♥ icon, select work, and while it still says "away" press the B button, and you'll be at your job! I really hope this helps! ^_^