I disagree, a CMS is a combination of pretty much every programming concept mashed together. While it seems to be the popular thing to advise, this is not suitable for a beginner who is just learning each concept. Putting the concepts together will really only be useful for someone who already knows each concept.

If you are a beginner, think of a practical use for each concept you just learned. You may have a to learn a thing or two more to complete that particular application but that is OK. Once you've learned everything then you might benefit form trying to make a CMS, but even then I think it is a complete waste of time.