Both, depending on what you want to say. "Some books" means there is more than one book, but you don't know/don't want to mention the exact number. This is about quantity. Example: There are some books on the table. "Some book" (without the "s") means you don't know, don't remember, or don't want to mention the name. This is about the name. Example: I don't remember where I read that; it was probably in some book or other. Or: The quote is from some book, but I'm not sure which one.

If you were to say to me "I am carrying Some Books..." I would assume you are carrying multiple books. If you said "I am carrying some book..." I would think you are carrying a singular book that you don't know the title of.

It's "Some books "🌸

There are some books.

Some books is correct