To sign up for Zoom Cloud HD on a computer, users go to the Zoom website and sign up using an email or Facebook account. An email confirmation is sent, and users must click the link in the email to activate their account and create a password. For iPhone or iPad, users download the Zoom app from the App Store and log in with an email or Facebook account after downloading. The document provides instructions for hosting or joining meetings, sharing screens to view documents, and ending meetings.