[AWBenson]

Simply put, you will move each bone individually for every movement. This usually takes more time to use, but you gain specific control over how each bone moves, rather it is realistic or not. Also, FK adds alot of keyframes to the timeline, so re-editing yourself can assigning graph editor curves take more work.

But, I wouldn't worry about it. This is a basic lesson about animation for your school. You will learn when it is better to use FK over IK through practice and time. As for IK, your school will teach it to your probablly later this class or the next one.