I am not an expert at all, but I did manage to configure Cacti a while back by fluke to graph some things at home. Here is a brief overview of what you need to do in the admin interface:

1) Management -> Devices -> 'Add' (hidden away in the top right of the page). Give it a name, put in the device's hostname or IP, SNMP details and hit Create.

2) Click on the device you just created in the list and add some 'Associated Data Queries' such as 'SNMP - Interface Statistics' etc. If you have some of these working with more than 0 items, you can click the link at the top that says 'Create Graphs for this Host'.

3) You can now choose a graph type and data query, click create and hope it works. I honestly can't really remember some of the details of how I got it working, but I do remember it took some determination to get it going and a little bit of trial and error as well.

Back in the day I had actually created my own Data Input Method which was a few lines of Perl that ran lmsensors and displayed the values correctly formatted for Cacti. This fed into a Graph template which I had created too. This was back in the day of my Abit BP6, so about 12 years ago! It did work well, eventually.