The first place to look is in the Perl documentation, of course. http://perldoc.com or type "perldoc" at your favorite shell's command line.

eval $some_perl_source;
[download]

do "filename.pl";
[download]

require "filename.pm";
[download]

use Packagename;
[download]

I would say that these examples are roughly in order of "maturity." By that, I mean, more mature projects tend to use methods further down in this list, rather than methods earlier in this list.

Whether it's a good idea depends on what you want to accomplish, where you get the code you've got, how much your sub-script needs to be isolated or integrated within the current script, and how much you trust the code you're running to do what you expect and nothing tricky.