Creating my own material GTIN problems

Hi
Like lots of people here i’m a bit confused to say the least.

I want to sell material that i have created myself in the form of looseleaf booklets to act as study aids for students in the UK. Revisions aids for GCSE’s and A levels etc.

It’s all my own stuff that i’ve typed up and written myself, its not published anywhere and am just wanting to sell them on Amazon.

I’m on the create a listing screen and i cant get past the Product ID section.

Do i need to apply for a GTIN exemption and if so, do i have to send Amazon a letter stating i authorise myself to sell the material?

I’m finding this really confusing?

Thanks in Advance.
Andy