Once it has started, the toploop window is where all commands should be entered for immediate evaluation. Tool-tip help is available for all of the buttons (move the cursor over the icon and wait briefly for a description to pop up), and on-line help is available. The most useful buttons are probably the evaluate-selection and evaluate-form icons (the ones with the => arrow in them). The latter will evaluate a definition or form in another window, if you've opened a file or new window for editing.
If you don't have an account, I've been told the following:
1) Non-CS students need to fill out an account request form, available from the CS office receptionist. Password information can be picked up from the receptionist the day after the completed form is turned in, and a student ID number needs to be supplied so your ID can open the PC lab doors.
2) CS grad students who don't already have CSEPCLAB accounts should send email to support@cs. You might want to wait on this for a while, however, as we may be able to have the appropriate directory exported to the CSERESEARCH domain. If you already have a CSERESEARCH domain account, that may be sufficient--I'll send out an announcement to the mailing list.