Best way to actually make projects?
Okay so i know some languages like phyton C# and C++ and im a computer engineering 1st year student but i dont know how to start big projects. I want to build a portfolio with some projects to also try out different ways i can go with computer engineering. I already do some embedding stuff, its the easiest for me but for example i want to make a 3D Physics Engine on my own but i dont know how. I already took linear algebra and physics I-II, i know the calculations etc. i need to apply but i dont know how to choose the programming language, or the API's, what to include, where to start etc.
Same for my minimal OS and netwroking project where i wanted to code a small OS with a shell and kernel and stuff and try networking between devices on that OS. But i dont know where to start, if i watch youtube tutorials i actually dont understand anything and it feels like i am just copy pasting.
I tried reading from documents from people who also did these projects but then again, i didn't understand anything and most of them just showed the whole code together instead of showing the steps they took to achieve that code.
I can use AI to write the code and i can implement it myself, i can just ask it the pieces of code and what they do, i actually did that too but i mean i dont actually know how to make one from scratch again.
I dont want to spend these years wasting time and want to make some projects but after staring at the shell i literally copied form a tutorial for an hour i noticed this isnt the way, Please help