Puppet package installation on Linux/CentOS

I am new to Puppet – I have been playing around learning the basics. Most of the examples ( except the very basic ones ) that are on the puppet page do not work for me – either some dependency is missing or package is not found. I do not see the logs explaining what went wrong ( even if I run the --test or --verbose option)

1. Can anyone clarify how does puppet manage to install any given package from a title ( for example starting from a manifest as below :

   class httpd {
         package { 'httpd':
              ensure => installed,
         }
   }
   

   Here – starting from 'httpd' – what happens when we run
   puppet apply on this manifest ? Where does it find the installer ( ie where is the repository – where is it configured ? )

2. Specifically , I am getting this error :

   err: /Stage[main]/Ntp/Package[httpd]/ensure: change from absent to present failed: Execution of '/usr/bin/yum -d 0 -e 0 -y install httpd' returned 1: Error: failure: repodata/filelists.xml.gz from base: [Errno 256] No more mirrors to try.
   You could try using --skip-broken to work around the problem
   You could try running: package-cleanup --problems
                          package-cleanup --dupes
                          rpm -Va --nofiles --nodigest
   

How can I fix this ?