Dartmouth has a site license for Mathematica Online. To log in using your Dartmouth credentials, navigate to https://dartgo.org/mathematica ( https://account.wolfram.com/login/oauth2/sign-in ) and use your Dartmouth College email address.
Click 'Dartmouth College', and then wait while the SSO system works to log in and provision an account. Next, navigate to Mathematica Online by pointing your browser to https://www.wolframcloud.com/