Nessus is pretty straight forward to learn, and set up.

1) Run the server
2) Connect to the server
3) Select the scanning policy you want to use, or create your own.
4) Input target, and start the scan.
5) Look at the results.

There is of course, a few settings you may want to look into (just browse through them). Generally it's a quite intuitive interface and easy to learn as well, if you just try it against a local machine on your own network.

About guides or articles, try: SecurityTube, YouTube, or just google for "Nessus guide", or something similar. Your best shot at learning Nessus would probably be, to check out the tool yourself.

IF you want to write addons / plugins, I'd recommend the documentation. Enjoy! 

Hi Hurtl0cker,


Welcome!

The best way I find to learn is to play with it, whats the worst that can happen ? set up a Vm of XP no services packs use Backtrack and just click stuff see what happens. if it break then just roll the vm back.

There are lots useful links to site on setting up a VM lab there are also many good books that have been mentioned before on the forums like

Gray hat hacking
hacking the next generation
web hackers handbook
professional penetration testing
CEH study guide will give you good understanding of the basic stuff
Counter hack reloaded
dissecting the hack the forbidden network
gray hat python

Also what about doing a course like hackingdojo or elearnsecurity

Thanks for the guidance guys
Started to play with Nessus, as MaXe mentioned it seems like  a pretty straight forward tool..
if  any  problems at all I'll post it here .. and yeah I'll try first and then post it here, after  all there is nothing wrong with messing around with stuff  .