If you are a new user, you can use the form on the SDF Home page, or from a shell, ssh to 'new@sdf.org' to create a new account.

You can normally just log in to 'sdf.org' for your use of SDF, but there are several servers, most of which, as a group, are known to SDFers as “The Cluster” (this term does not include the metaarray). These servers are listed in the SDF FAQ: WHAT MACHINE DO I LOG INTO FOR SHELL ACCESS?