I agree with Susanne, that without context it would be difficult to give a sure answer to this question.
As the question is asked in the present tense, it could imply simply as to how you feel when you're teaching. To this you would have to answer specifically, but could be how you approach, present and manage your position of teaching.
If the context is as Susanne assumed, then it should really be asked in the past tense. How did you find yourself teaching, or in a teaching position. To which you can explain your history of education and why you decided to seek a career in teaching.
Hope that helps,