dollar sign ($)
'cu' stands for Call Unix. It used to be used for calling dialup services from one Unix to another. Hardly used anymore with networks (which are much faster)
Unix came first; Linux is a clone of the Unix Operating System.
For example struct tm and struct stat are often used by UNIX processes.
Unix is used very similarly to other operating systems (Windows, etc.) for their applications.
The question is rather vague; the applications used in Unix are similar or identical to those used in other operating systems, such as Windows.
Unix internals refer to the algorithms and techniques used by the resident operating system to manage resources.
The lp and lpr commands are the traditional commands used to print jobs on UNIX.
A Unix shell can be obtained in Cygwin, a Unix compatibility layer used to compile Unix programs and run them on Windows. Microsoft also makes a shell known as "Windows PowerShell" which incorporates more Unix-like features than the standard command prompt.
In Unix, use the 'man' command.
The pipe symbol is a vertical bar (|), not a forward slash.
In Windows: "", the so-called backslash. Usually after the drive name, as in "C:" In Linux and UNIX: "/", the slash.