Don't worry, the Win RT/8 interface isn't necessarily easy for some people to learn simply due to more functionality; the more functions there are, the more complex the array of possible interface commands.
The "aren't readable" issue may be anything from DRM to format, which is a bit harder to troubleshoot without screenshots and some terminology, but as for deletion...
File interaction in the Windows RT/8 "Modern" interface, meaning the new Start Screen and "Modern"-designed apps, includes special swipe gestures from all four edges of the screen. This is different from both iOS/Android. There are also special gestures within such apps, and one would be file selection.
A typical generic example would be the Photos (photo album) app. If you simply press a thumbnail, the app will open the image to see the full size. But if you want to do "file management" with the photos, you have to do a quick swipe down on the file, which
selects it. Then, a simple bar "menu" of options will show up on the bottom of the screen, allowing you to actually manage the file (e.g. delete, select all, import, etc.).
Touchscreen gestures for Surface | Zoom, scroll, and tap
Microsoft does have tips and tutorials on their website, including a downloadable manual, but I highly recommend searching Youtube for tips because it's just much easier to see how these things work in "motion." I watched a short 3-minute video before buying my RT and learned all the swipe gestures and multitasking that way.
Edit to add: I don't know about the free downloads thing, mainly because nearly all my documents are PDF papers that I have to move around locally. If you're attempting to download DRM-free books in the web browser, I think they will save in the default Downloads folder unless otherwise specified. Then you'd have to find the folder while using the book reader apps, or find the downloads in Windows Explorer and move them to a folder of your choosing (I recommend finding a well-reviewed file manager/explorer app in the store because the "Modern" interface is easier to use with fingers).