Hi @theeo123
I´ve been in the same position since moving from Cura to BambuSlicer. It is way more straightforward, and you´ll get used to it in time.
Starting with the last question, which you could have in Cura, the 0.12mm fine and high-quality are just two printing profiles (aka settings) with a standard 0.12mm layer height. You could do the same and call whatever you want. Both are stock presets, with the fine being available longer.
To check the difference between any printing present, you can use the Bambu Studio, using the compare presets button:
Then, select the second preset to compare with:
In this case, the high-quality profile differs from the fine one regarding lower printing speeds and gyroid infill.
You can extend this to different filaments and printers (or nozzle sizes).
A preset sets specific settings for different groups: printer, physical printer, filament, and print settings.
This kind of layout may feel complex and, in some cases, pointless. But it seems pretty robust when there are multiple printers, filaments, etc, as it facilitates the definition of printing settings dependencies.