Can you try explaining to me again why I need to compile my own and why I can't use a packaged version?

If you are just going to use perl and the packaged installation provides what you need (maybe all you need is the core distribution if you are just beginning to learn Perl), then you can certainly use the packaged version of perl.

If you want to add or update modules and you are using the packaged version that came with your system, then you should use your systems package management to add or update the modules. As long as you stick to your system's package management system, you should not have any problems. Many of the commonly used packages from CPAN are available from the package management system for ubuntu/debian based systems and you may not need anything else.

If you use the perl provided by your systems package management system (/usr/bin/perl), then you should be cautious about installing or upgrading modules from CPAN independently of the package management system. You can end up with conflicts that are hard to resolve. Some parts of your ubuntu (I am assuming umbunto is a typo) system depend on perl and you might even break these. This is the root cause of the advice to install your own perl.

If you want freedom to change the configuration of perl and install modules from CPAN that are not available from your package management system, then you will minimize the risk of problems arising from interference with your system's package management and the requirements of other applications which presume perl will be as installed by the package management system, if you build perl from source yourself and install it to an alternate location. But, if you are just beginning to learn about Perl and Linux you will have quite a bit to learn and even the "simple" task of installing the required tools, compiling and installing perl and learning how cpan works may be more than you want to tackle just now. It's easy, once you know everything you need to know, but a bit mysterious and time consuming until you do.