Ah, Tinah!

The joys of new ownership. I remember them well.

Only took me 2 months or so to find my way around. And I have another ereader, which helped.
Let's see . . . . Did you buy the book? If so, tap Reader, then tap Open from Storage (I think). If you have to look for it, look in the Downloads folder. It should look like a blue book and (hopefully) show the title. Once you find it you can tap it and the book will open on the e-ink side. Once you have it there you can add it to your library or just read it, whichever.
If you downloaded the Kobo reader for Android software and your book is in that I don't know where it will be. There might be a folder just for Kobo books in your Storage section, and you might not be able to get it onto the e-ink side. If this is the case I or someone else can help you more. I go through my PC and either Calibre or Adobe Digital Editions to get my books.
Enjoy!!!