Answer 1

Maybe he is not best teacher, maybe you are right, he's confusing, skips a lot of things... but don't be hard on teachers, because teaching C++ or any programming language is really difficult. There are probably so many things he could show you but his time is limited so he can't go to all details. Fortunately you have internet, try to do a little bit of research by yourself, and if you have a question you can always ask teachers. I think that's one of the best things in school, you can ask teacher anything you want (if you are not shy ☺️) about programming. Have patience, as Gustav A C/D C ☢️ TBTF teachers are humans too and they are still learning.
In case you are interested in C++ and want to know almost every detail then check this website:
https://www.learncpp.com/

Answer 2

See if your teacher does not explain you in a proper way then you can complain to your head of department (HOD).

Btw don't worry about your marks. Sololearn is the best option to learn technology. But here is only basics given so I am sharing a link to you where you can learn much.

https://code.sololearn.com/W71i1t1MPVp6/?ref=app