"sudo" says to run the next command as the root user. "perl" starts the perl interpreter, and automatically loads in a module called "CPAN" ("-MCPAN" is equivalent to "use CPAN;"). Finally, "-e" is the "execute this perl code" command, and we're saying to execute the "shell" command of CPAN.
The second command installs the actual module. If you know your module name, you can use it - so "install XML::Parser", "install LWP::Simple", "install DBI::mysql", and so on and so forth. If you do the "Bundle::DBD::mysql" as above, then you don't have to worry about installing the matching DBI module - it's contained within this "Bundle".