Hello and welcome to MobileRead!
Your wife should be able to purchase and download books from the Kobo store directly on her Kobo Clara. As you say you are not computer people, that's certainly the easiest way for her to obtain books.
As to Amazon books, they cannot be read on a Kobo without removing the DRM (which is illegal in many countries) and converting. It's not allowed to discuss the DRM removal in detail here. Visit the Apprentice Alf's blog (
https://apprenticealf.wordpress.com/) to learn more if you want to read Amazon books on the Kobo.
Free books are mostly public domain (i.e. their copyright has expired) and can be downloaded from Project Gutenberg or from the ebooks section here (
https://www.mobileread.com/forums/fo...play.php?f=132).
Hope that helps.