Some students finish their undergraduate programs and want more.
If you want additional knowledge, if you want to hone your expertise and study a specific aspect of your field in greater depth, then graduate school may be for you. In agriculture and biology, this usually means two or more years of study and research, and with a different academic approach than that you are used to as an undergraduate. But as a graduate student the emphasis shifts from sideline watcher to active participant. As an undergraduate, you mostly learned of others contributions to humanity's body of knowledge. As a graduate student, you will make your own contribution.