These manipulate a scalar's value without needing two elements in an equation. Some people like them, some don't. I like the fact that they can make code clearer. Strings in Perl don't have quite as much flexibility. Just remember, the plus sign adds numbers and the period puts strings together .
Arrays are lists of scalars.
You can also modify it in place, just like any other scalar. If an array doesn't exist, by the way, you'll create it when you try to assign a value to one of its elements. This is one less than the number of elements in the array. Each key in a hash has one and only one corresponding value. It's a leap year.