When it is necessary to use language elements that have not yet been thoroughly explained, you will usually find a comment telling you that this concept will be covered later.
With that in mind, remember that the order of the lessons has been carefully chosen to give you the foundation for each lesson before it is presented. Sometimes that's a very difficult thing to do, because it's hard to explain arrays without explaining scalars first, and yet there are distinctions in scalars that require arrays to explain.

Perl is a dynamic programming language created by Larry Wall and first released in 1987.
Perl borrows features from a variety of other languages including C, shell scripting (sh), AWK, sed and Lisp.
Structurally, Perl is based on the brace-delimited block style of AWK and C, and was widely adopted for its strengths in string processing and lack of the arbitrary limitations of many scripting languages at the time.