Sorry running a little late today.
The ISBN- is the International Standard Book Number. To you the reader it is that weird barcode on the back of the book with 13 numbers or 10 numbers usually starting with a 9. This code helps booksellers sell your book in stores. You can buy an ISBN for your book it can be over $100, but get this you can get them for free.
Smashwords, Createspace, Kindle Direct, and Nook Press will give you a random ISBN number or an ASIN (Amazon Standard Identification Number) number.
On a side note I was a bookseller for 6 years. I dubbed us book nerds ISBNs (I am a Super Book Nerd). The sounds of scanning barcodes still haunt me to this day.
Tomorrow I will talk about copyrights…
And just a reminder, if you have any questions please leave me a message or email me at firstname.lastname@example.org. I am always willing to help new writers, even if it is to point them in the right direction.