Please help to create a multi-menu MessageBox

[Sergeek]

I am at loss. I read the Guide at wiki and another one at Nexus, but they are so complicated, and they only got me so far...

I want to make a book that prompts a MessageBox (above its actual contents, like in Oghma Infinium) with four initial choices when you read it both from the floor and from the inventory (hence both Activate and Equip beginnings). These choices being the three skill specializations and "exit" button. Upon clicking the specializations, another menu should appear with seven respective skills plus the "back" button. Each skill button should increase the respective skill with ModPCSkill command by one, while keeping you inside the same specialization menu. The "back" button should return you to the initial menu where you select specializations. It is way beyond my understanding. I only managed to make a single-layer menu that keeps you inside of it, when you choose the first three options.

ScriptName MyBook

short Choosing
short Choice

Begin OnActivate

    Activate
    Set Choosing to 1

End

Begin OnEquip

    Set Choosing to 1

End

Begin MenuMode

    If ( Choosing == 1 )
        MessageBox "Select Specializations", "Combat", "Magic", "Stealth", "Exit"
        Set Choosing to 2
        Set Choice to -1
    ElseIf ( Choosing == 2 )
        If ( Choice == -1 )
            Set Choice to GetButtonPressed
        ElseIf ( Choice == 0 )
            Set Choosing to 1
        ElseIf ( Choice == 1 )
            Set Choosing to 1
        ElseIf ( Choice == 2 )
            Set Choosing to 1
        ElseIf ( Choice == 3 )
            Set Choosing to 0
        EndIf
    EndIf

    If ( Choosing == 0 )
        return
    EndIf

End

Please, I have no background in coding and any feedback will be greatly appreciated.