1. See CGI, and possibly some of the templating modules such as Template.
2. See system, exec, and the Quote-Like Operators section of perlop (specifically qx() and ``).
3. This step will most likely be integrated with step one, using the templating modules (or CGI.pm's HTML generating functions... if you're in to that sort of thing).

And, of course, I second barrd's recommendation to read Ovid's course.