Navigate to the following link:
If you have previously created an account to download Mathematica using your Davidson email address, log into it here. Otherwise, choose the option to create a Wolfram account.
It will ask for your name, email (you must use your @davidson.edu address!), department (pick your major) and anticipated graduation date. (The Product and Version will be automatically filled out for you)
Upon submission, Wolfram will email you an activation key and a download link that will walk you through the installation.