Hi Birgit

You touch on a lot of things here! 

However, it certainly makes sense to separate content from presentation i.e. the actual words, images etc. from how they end up looking and being arranged on the web page.

If you know any HTML (and if you don't, even as a non-techie it's worth learning the basics) you'll realise that it is a mark up language - you can make any basic, non-formatted word (the 'content') look however you want e.g. change its font, colour and so on. 

Ideally you would have your content (including media assets like sound files and videos) sitting in a database and these would be pulled onto the web page using a template, and CSS for design/layout, that is in your CMS. 

So Design would be a function of the template and the CSS. The content is the raw materials which sit in the database. 

The structure has potentially many levels. It often gets called 'information architecture'. The two most obvious and basic forms are a) the information architecture as experienced by a browser of your site i.e. the navigation / sitemap and b) the metadata you use to categorise and strucuture and tag your content in the back end. The latter is perhaps less often thought about, and not *directly* part of the user experience, but absolutely vital to running a site efficiently. 

Ashley