Hilary, forgive me if this is too simple for you (I suspect by now you are a much more sophisticated user than you let on . . .

), but here is what (little!) I know to do in Moonreader:
Open Moonreader+. It should show your last page read. Push the Menu button. This brings up a top row with a download button (gets you into file explorer to load your next book), the title, % read and a percentage slider (presumably for moving around in the book -- I don't want to try it

). Also you get a bottom row of icons, including -- left to right -- the orientation switcher (

), night/day toggle, an auto-scroll starter, a bookmark finder icon (note to self -- must learn more about this!), a table of contents icon, and a settings icon. Tap any of these for its functions and when you are done you will be back to your reading view.
Tapping the Settings icon gets you into a world of menus.

I was suggesting you explore these menus (visual options, control options, miscellaneous, themes, more operations, about Moon+ Reader, and exit reader) to find what you like about the application. For instance, I like the gradations of blue with a white tree in the bottom right corner for my day screen. I made it a theme, overwriting the old day theme, and now when I switch from day to night to day I come back to my favorite blue. I also told the program (app -- sorry!) to let me change font sizes by scrolling up or down the far right side and to change brightness by scrolling the left side.
That's probably enough verbiage from me!

Let me know if any of it is helpful.