A trouble with design of game project

I have a trouble. I'm learning programming with in home and university about one year. Now, in summer, I studying on the free courses called "Summer school" in one friendly IT-company. I developing ascii-roguelike in Terminal using CXX lang and NCurses library for Linux. We were advised to use the Entity-Component-System design pattern. Or, at a minimum, it's good to design a good class hierarchy. And also use other patterns, such as the prototype, IOC container, State Machine, Route Machine, and so on. To date, I'm in an absolute dead end: I have a ready-made piece of the game, but everything in it is very strongly connected. I absolutely do not know where to start, the implementation of the ESC looks very complicated, today I spent a whole day reading articles and code, in the end I did nothing at all. Advise, where to start, what to do? Can I draw a diagram of entities, components and systems on paper? Or how, what? There is a poorly written piece of the game, there is a clear task, there are recommendations for patterns that are desirable to use, there are teachers who do not explain for hours, they need to be approached with good questions. Maybe someone has something to share, to help.

PS sorry for my bad language