Question;
I know my way around HTML and CSS (or SASS) but how do I connect my site to a CMS? So people can update their site i build for them, I don't want to keep updating their site in the HTML code every time. I can't seem to find a good connection (tutorial) on how to make this happen.<p>Hopefully you have some examples of how to connect my HTML designs to a (free) CMS.<p>Much appreciated!
HTML and CSS alone would not be adequate for the kind of behaviour you are looking for - 'updating their site'. At the very least, you need to learn how to customise a CMS. A well known CMS that I would recommend is WordPress. However, there are others in other languages/platforms. But, since you are talking of a CMS, I thought I should point you towards the most widely used one. Thus, you need to invest your time in learning how that CMS works and what you need to do to customise it for your clients. You might also need to learn something about databases and MySQL would also be another good recommendation.
I would say that you need to start looking into frameworks if your goal is to build a custom CMS. I have done this on many production projects using the MEAN stack (MySQL, Loopback, Ng2, and Node). There is a lot to take on if you go this route if you are not familiar with any of these. I would suggest starting with Loopback + Node, and then move to Ng2. If this is to overwhelming, I would focus a lot on @sdiq points :)