On the resulting page, under "How would you like to receive your copy of Mathematica", select option "Download: Send it to me at the email address I specify (you will be asked for your email address later)"
Then, under "For what platform will you need your home-use license?", select the option for the platform you will be using at home
On the resulting page, fill in your contact information in all the starred boxes
In the "Email address" box, fill in your Cornell email address ("netid"@cornell.edu - substitute your Cornell Net ID for "netid")
In the "Work Address" section, fill in Cornell University for Organization name, CLASSE for Department, your office # (eg: 310 Newman Lab) for Address, Ithaca for City, NY for State, and 14853 for ZIP/Postal code
In the "Proof of Eligibility" section, fill in https://www.cornell.edu/search/people.cfm?netid="netid" (substitute your Cornell Net ID for "netid")
Note that the Activation Key you will receive will be valid for 15 calendar days without action by the CU Software office. Within 5 business days of receipt of the key, a representative from CU Software will verify the registration and will extend it through the end of the license period, which ends on 31 July.
Once you get your email from Wolfram with your activation key, activate Mathematica as follows:
Navigate in the toolbar to Mathematica ► About Mathematica.
Click your activation key (just above the "system Information" button) to access the Mathematica activation dialog.
Copy your 13 digit activation key from the Wolfram email and paste it in the appropriate field in the activation dialog