Before installing Munin on server01 apache2 will need to be installed. The default configuration is fine for running a munin server. For more information see HTTPD - Apache2 Web Server.
First, on server01 install munin. In a terminal enter:
sudo apt-get install munin
Now on server02 install the munin-node package:
sudo apt-get install munin-node
On server01 edit the /etc/munin/munin.conf adding the IP address for server02:
## First our "normal" host. [server02] address 172.18.100.101
Replace server02 and 172.18.100.101 with the actual hostname and IP address for your server.
Next, configure munin-node on server02. Edit /etc/munin/munin-node.conf to allow access by server01:
Replace ^172\.18\.100\.100$ with IP address for your munin server.
Now restart munin-node on server02 for the changes to take effect:
sudo service munin-node restart
Finally, in a browser go to http://server01/munin, and you should see links to nice graphs displaying information from the standard munin-plugins for disk, network, processes, and system.
Since this is a new install it may take some time for the graphs to display anything useful.
The munin-plugins-extra package contains performance checks additional services such as DNS, DHCP, Samba, etc. To install the package, from a terminal enter:
sudo apt-get install munin-plugins-extra
Be sure to install the package on both the server and node machines.
See the Munin website for more details.
Specifically the Munin Documentation page includes information on additional plugins, writing plugins, etc.
Also, there is a book in German by Open Source Press: Munin Graphisches Netzwerk- und System-Monitoring.
Another resource is the Munin Ubuntu Wiki page.