The while loop puts each line in $_ which is some sort of universal default variable.

The split splits the string in $_ on the following pattern: "zero or more spaces; equal sign; zero or more spaces" and puts the results of this splitting in the variables $key and $value (actually $value is not used in my script, but I left it in otherwise you might wonder where the second part of the split went to).

m/["']([^'"]+)/ is a regular expression match and it (also) does some pattern matching, again on the contents of the $_ variable. It tries to match the following pattern: "one single or one double quote; one or more times anything but a single or double quote". The "one or more times anything but a single or double quote" pattern is captured (see the parentheses round the [^'"]?) into the $1 variable. If the match succeeds, we store the contents of $1 into the %data hash keyed by $key.