"Scríobh" means either "write" or "wrote" depending on context?
If you mean the imperative, yes. If there's a pronoun following it, odds are it won't be the imperative.
I'm confused I thought this said "I write a book" because what we learned about past said it would be lenited if it was past.
<sc> is a combination that can't be lenited. If it could, it would sound like <hc>. Try saying that fast!
Oh right, I think I remember reading that before. So you would never use "Scríobh mé" for "I write" you would always use "Scriobhaim" and then you can tell present from past. Go raibh maith agat!