In addition to the basics, it seems worth explaining 'why use perl?', which can only be answered by mentioning features which are unique to perl, such as:

- the many replacement functions for shell or DOS commands and C functions that avoid spawning to such scripts and programs.

- the huge wealth of modules in CPAN

- the relative flexibility of storage ("typeless" scalars, arrays and hashes)

- adaptability of programming style and system level (OO, event-driven, data-driven, database interfaces, operating system call interfaces)

Others might be able to suggest additions to this list.