First, you have to clarify by what you mean by "create social networks" - that's a pretty general term.
Perl was originally designed as a reporting language, and through the years its been adapted and extended to handle most tasks. Its a bit long in the tooth, IMHO, and is showing its age. It's much easier to do certain things (like handle database connections) in PHP or Ruby or Java. Perl definitely has its place, but if you're new to web programming I'd recommend you start with the basics of HTML, PHP, CSS and JavaScript.
