It is a very important question and just make sure you go in a correct flow according to me you should first define Manifests.
Every node (or Puppet Agent) has got its configuration details in Puppet Master, written in the native Puppet language. These details are written in the language which Puppet can understand and are termed as Manifests. Manifests are composed of Puppet code and their filenames use the .pp extension.
Now give an example, you can write a manifest in Puppet Master that creates a file and installs apache on all Puppet Agents (Slaves) connected to the Puppet Master.