An advanced degree is required for some jobs, such as being a college professor. It also gives you the opportunity to study a topic of interest to you in depth and from a research perspective.
See the University of Wisconsin-Madison's Graduate School Steps to Apply page. They do a fabulous job outlining the times at which you need to complete the various steps to apply. These will be similar at other schools, but you should check for specific dates for each institution.
Some good places to start your search are:
In considering graduate schools, these articles can help guide your thinking:
Here are several resources to get you started on the process. I am also very happy to review your essays one-on-one and give some feedback. You could also take them to the Writing Center here on campus.