Some of Yale's internal tools, such as the cluster, are only available on the Yale network. If you are off campus, you will need to use a VPN. For Windows and Mac OS X, download the Cisco AnyConnect VPN Client from the ITS Software Library. See this guide for Linux and for the full instructions, which will be briefly outlined below.
Once you have installed the Cisco software, type in the server address: access.yale.edu and click connect. This should open an authentication tab in your browser, where you will be able to log in using your Yale net ID and password.