If you have a grip on html then it is not always essential that you need a CMS to edit your site, a perfect CSS could do the trick!
A perfectly coded CSS site gives you the flexiblity to edit anything on your site. But if you are not a techie then opting for a user friendly CMS software would be a good idea.
Depending on the technical expertize people prefer joomla, wordpress or concrete all of them have thier own advantages! And in case your site is its custom requirements and wont fit into either of the above mentioned third party softwares then you should go for a hand built CMS.