Understanding WordPress rewrite

Hey!
For intro, I don’t really know, if I’m doing it right way, but I’am making new section, like inside social network of my school, where would be all classes, and classmates would write new discussions, add galleries, share their experience at school etc. This wouldn’t be joined with wp-admin engine, and I’m coding my own.
I don’t know, how to explain what I’m doing, but it kinda works for me, as it should, and I hope you understand it from intro ??

Anyway, I have problems understanding, how to create and use URL rewrite features for my project.

I have Page “Classes”, and using my new build theme for it. Writing like new homepage, using WordPress as base.

And, for example, at sidebar, I have list of classes, where are like 5a, 5b, 6a, 6b … 12b, 12c and so. Clicking on link, it leads to this classroom, where you can see all content, what that classmates have made. All this stuff works great, and don’t worry about security – it’s all covered ??

But here comes the question.

https://localhost/liepa6vsk/klases/?class_id=5 this link stands for class, which name is 7a. I want to make that I shouldn’t use ?class_id=5 to recognize that class. I want to make friendly URL, like https://localhost/liepa6vsk/klases/5a/ and it still recognize, which page should be displayed (by class_id which is 5).

Looking at .htaccess file, I can’t figure it out, how does this stuff works… Actually, I never spent too much effort to understand htaccess… ?? But practice makes you perfect, and if you, buddies, could help me, it would make me perfect ??
And yeah, of course, when somebody will be inside in that virtual classroom, there will be like other sections. For example ?class_id=5&discussion_id=123. And I want to make to /7a/discussion-name/.

I hope, that someone could help me.

If needed some more information, if I didn’t explained something clear, be welcome, and post comment here.

Anyway, thanks.

/Rob