I have been using Silverstripe for almost 12 months now but after a brief foray into Joomla recently I see I have not been using it properly. I currently do everything via the WYSIWYG editor and moving everything manually when it needs to move to another area.

In Joomla, I write an article, assign it to category and I can change that category. Where on earth is that function on here as I haven't found it. I am a complete newbie to CMS and am not sure I have the know how to use Silverstripe.

Is silverstripe on a par with Joomla with regards to skill levels or is Silverstripe just for serious developers?

It sounds like you're doing two different things with two different CMS's. If you fired up a third CMS you'd probably find it was different again.

To have articles in Silverstripe with the functionality you describe in Joomla you would create a new page type or dataobject with fields such as category so that content could be organised in this manner.

Out of the box, Joomla probably offers more options and has a load of modules that are easily installed. Silverstripe, on the other hand, has a greater learning curve but is much nicer (IMO) to develop for when it comes to customising the CMS.