Nokia 3310 / 5510 LCD assistance without library

I would love to use the libraries...

if they worked. I'm not understanding how for an LCD screen so common, with LOTS of different libraries for it, I cannot find one that will work.

However, I would like to gain an understanding to how make an LCD screen work without the use of a library so I can make use of the other LCD screens I have that do not have publicly available libraries for, like a couple of these larger Optrex 30x4 screens I have.

And going about this project this way, I don't have to stick with one LCD screen, I can change screens without changing many lines of code.