A content management system (CMS) is a system that allows you to manage the content of your website. Most CMS's allow you to do this using nothing but a web enabled browser - ie you can use Firefox or Internet Explorer as long as you are connected to the internet. This type of system is an example of a 'web app' - website application. Facebook is one such web app you may have heard of, or even Hotmail.
There are literally thousands of CMS's to choose from. I chose to specialise in Joomla! back in 2006 and am thankfull that I did. It has come along way, here are a few stats...
Some of the higher profile companies / institutions that use Joomla include
My personal rule is that if you are capable of sending an attachment in an email you are highly likely to find Joomla easy to use. If you use Facebook, Hotmail and so on then it will be no worries at all.
Joomla is free! It's a peace of Open source software realeased under the General Public License Version 2.
If you wan tto know more about Joomla or even have a go at using it then here are some usefull links for you:
Long ago I started using the JCE content editor for Joomla on all my clients Joomla websites. It greatly expands on the default editor. It is has many features including:
You can read more about JCE or even try it out yourself here.
Below is a screenshot of me using JCE to type out this page

Well there is not much point having a website if no one can find it. That is why I do all basic search engine optimisation as standard.
I use a Joomla extension called sh404sef. Basically it means that all the addresses of your website will be easy to read for both search engines and sentient bipeds such as humans.
Here are some of the SEO (Search Engine Optimisation) steps I take:

Unless you specifically request otherwise I always provide my clients with custom made video tutorials on how to manage thier website.
These videos will be on your website and are accessed using a username and password. Below is an example:
Please note the video's would usually be magnified a little more than this one.
In addition to the backup system most likely provided by your webhost I now install and configure 'Joomla Pack' on all my clients websites. This allows for backups to be made easily, lets you enter notes for each backup and amongst many other other options allows you to exclude certain folders.
Google Analytics is a free tool provided by the good people of Google. Basically it lets you see who's looking at what, when, where, how and what with on your website. It has so many features it can track almost anything. If you have a solid business and are not competing against every Tom, Dick and Harry then it is highly likely that your website will pay for itself in no time.
The record return on investment for a website that I have designed and built is currently 133 times the cost of the website was made back within 1yr of launching thier website! They also had other benefits including sourcing high quality staff directly without even mentioning jobs on their website.
The record time for a 'call to action' to happen is less than one week. In the end a lot of it depends on your business but you can be rest assured that you are in good hands.