At this point we should be able to ask you, "Well, what do you suppose those lines do?" And if you're unable to at least take a stab at it yourself, it means you didn't follow earlier advice to read the documentation.
At the command prompt type "perldoc -f push". Or (easier on the eyes): visit http://perldoc.perl.org and type in push.
Now try "perldoc perlreftut", and then do the same for perldsc, perlref. Read them. Ask about the parts you don't understand.
I'm not trying to be stubborn here, the questions in this thread are all indicators that you're trying to understand code without trying to understand the language the code is written in. We can tell you exactly what those lines are doing, but that would just be throwing good money after bad; someone's already written the documents, someone's already pointed you in their direction... I know that laziness is a virtue for Perl programmers (which is why the documentation was written in the first place), but asking others to read it and tell you what it says is false laziness -- it will be more work for you in the longrun if you have to ask each and every time.