The computer systems used by JCMT observers run Linux, which is a Unix-like operating system. If you are only familiar with (e.g.) Windows-based systems, it would be useful to learn at least a little about Linux before you observe at the JCMT. There are many excellent introductory online resources available for users. For example, one very good introduction is available here.
Note that if you have a Mac, then you already have access to a Unix operating system, as macOS is actually a certified Unix variant. The standard Unix commands that are commonly used are available via your Mac’s built-in “Terminal” application.