As a flight instructor you gain experience by teaching others to fly. This way you learn the material extremely well (learning by teaching) and you get paid to fly. This is a very common way to start a flying career in the United States.
The instructor certificates come with ratings limiting you to certain areas of instruction. A regular instructor for instance can only instruct private pilot and commercial pilot students on single engine aircraft. To do instrument instruction an instrument instructor rating (CFII) is needed.