This tutorial assumes you already have Cacti installed.
As far as I know, Cacti is available in Ubuntu repositories.
After installing it, you should also install cacti-spine, which is an upgrade to Cacti's default poller (poller.php). Spine is in C and it's much faster. Depending on the number of cpe's you're monitoring, as well as the poller cycle, spine turns out to be a must have.
If you're new to Cacti, it's highly recommended that you try to produce a basic graph (for example, cpu usage), one of the few bundled ones, before trying to produce the ones shown in the tutorial.
In that case, you probably need to install snmp, since those bundled grpahs use snmp as their data input method.
By producing a standard graph, you will validate your installation and make sure everything is ok.