The thing about Cubase is it has a 1,300 page manual.
The other thing is that, until you've read that manual at least 3 times, you're going to struggle.
All documentation is available via the Help Menu.
Everything is key-commandable - literally everything.
Every menu, every function, every user-made preset.
If you need harmonic transposition, then use the Transpose floater - ctrl/T to set it up & alt/T to action it.
If you need simple parallel transposition, then use the Logical Editor & make yourself some user-presets - that way you can transpose up or down without opening the edit floater again.