First off, I cringe every time I see PERL. So don't do that. Most often you mean 'Perl', the language (as opposed to 'perl' the interpreter).

In Perl a % at the front of something means the thing returns a hash. A hash is kinda like an array except that it contains key => value pairs. The split built the hash contents by generating an array of paired entries.

The for loop iterates over the keys for the hash %spl. Note that the keys are 'PROGEEK', 'GEEKS' and 'GFG'. The values happen to be numbers - they could be strings or other things.

Perl has a really nifty feature called 'interpolation' which replaces variables in a string with the content of the variable. The print uses interpolation in its string to print the key (in $i) followed by a colon (just boring text - no magic here) then the value in the %spl hash associated with the key in $i (that's the $spl{$i} bit).