[1.12.2]Making a custom book

[Skelyvelocirap]

Hello,

 

My mod is not yet finished(not even 1% completed) and its already getting quite complicated as the player to know what to do, as such i really want to add a guide in my mod to explain it a bit. My problem is... I have no clue how. I know how to make the actual item itself but not the GUI. In the GUI i also would like to have some specific slots that show what the item is, a bit like the book in openblocks. Also i should precise, i have looked at some examples of books but i honestly don't know how they work Please help, i would really like to have it work!

Thank you!