Cool! Good to see another DiabloRL player! :D
is there a help button...
Yes, if you push the Escape key in game, there's a menu that includes a help section.
...or a list of keybindings?
The help menu includes that and there's a file called keybindings.lua in the game folder that you can edit if you want to change them.
Some other useful things you can do: Q to bring up your belt (where you store extra potions/scrolls) and once that's brought up, you can push I to transfer items from your belt to your inventory, D to drop them, or Enter to use them. Similarly, when you bring up your inventory, you can use Q to transfer scrolls/potions to your belt or D to drop them. Pushing Tab while in inventory also lets you cycle through your worn items in case you want to take them off. (These are the default keys, of course; I'm sure you can change them)
So I am stuck in some sort of library.
I have an empty bookcase (got and read book of firebolt)
and an open book.
How do I read the open book?
I'm not quite sure what you mean here; you can read spellbooks you pick up by selecting them in your inventory, but it sounds like you already did that. What do you mean by "open book?" I mean sometimes, you encounter yellow books that provide a bit of extra background story when you walk into them, but I suspect that's not what you're talking about here. I think I need a bit more information.