Hello, I have just started to learn Perl.

Great. This is a good place to start, and you've picked a fun language to learn with.

Since you're just getting started, go to http://perldoc.perl.org and read perlintro. The question you're asking is addressed in the section titled, "Basic Syntax Overview". There it explains the rules regarding whitespace. But do read through that full document. It will hasten your learning experience, and takes advantage of the fact that many of the questions you're likely to come up with in the first few days have already been answered in one concise document.