On the munin server, include the munin class from the module (and optionally also include the munin::client):

node 'munin.example.org' {
    include munin
    include munin::client
}

On the munin client (the system to be monitored and profiled), include just the munin::client class:

node 'munin-node.example.org' {
    include munin::client
}