For Kobo you have to do it via your PC. You have to have something called Adobe Digital Editions (same if you purchase through Waterstones) on your pc (free download). Your book gets downloaded into that, then if you've got your device plugged into your pc, it shows up on the adobe page and you can click and drag your book across from the'bookshelf' on adobe digital to your ereader.
I have had a kindle for years now and it is brilliant. I have the app on my smartphone so if I am out and about and using a train or stuck in hairdressers etc I can open my book on the phone and it will have synced to where I had got up to on the Kindle.
Dual use and just great. Easy to read on either my kindle or the Samsung Galaxy which is smaller to put in handbag.
Like everything these days they are out of date almost as soon as you have slapped down the cash. But I would get another when mine goes the way of all old technology.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.