Are there any lessons on template layout for opencart 2?

Question

CMS

Hello. There was a task to make a store. I looked at the reviews: opencart had better ones than others. I looked at the source code, it turned out that everything is not as simple as it was in the reviews. In the same dle, atom-m, jmy, everything is much simpler, but, alas, they are not store engines. I rummaged around on the Internet, but did not find anything current. I would like them to show from beginning to end how everything works, and what they are responsible for. Can you advise something? Or can you recommend an engine (free) for a store that will be like dle?