You should have received an official notification from the Graduate School giving you basic information about how to access LOCUS in order to enroll in classes, etc.
As is explained in the letter, your first step is to go to http://luc.edu/gpem/
newadmit.shtml and look carefully at the advice and information on that page. This will help you to access LOCUS, which is where you will take care of registration and other functions. I recommend that you watch the Tutorial, since Locus can be a little tricky no matter how computer savvy you are.
Go to the link on the program website for the graduate courses offered in the coming Fall. Look carefully at the graduate offerings , as well as the 300 level courses. You may take 300 level undergraduate courses for graduate credit TWICE (two times in your MA program), so that might be an option as you enter. But remember that you can only do it for two courses.
A full time load is three courses. But you are not required to do that, if you are working, etc. You will need to take History 400 in the first year, either Fall or Spring semester.
By the start of the year, you will receive access to an Advisory form for your program (MA, PhD, etc.). This will be your road map as you progress through the program. We will be setting up a shared directory in "luc.box.com" where I will ask you to keep an updated version of this through your career here.
I would start in classes that are most consistent with your main interests, allowing you to get a strong start. All this said, you may also directly contact faculty in your area, who can give you some more detailed advice.