It is usually a good idea to Super Search before posting - this question is nearly a FAQ. A quick search identified these threads:

• Call one Perl Script from another (posted less than a week ago)
• Can a Perl Script call another perl script?

The short answer: system, exec, backticks (see perlop), qx//.

If, by "invoke" you mean use a module, then use, require, or do is usually the way to go. Again, the docs and Super Search will get you started.