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KOReader tries to take advantage of the features of the different platforms it runs on. So, there may be some slight differences in how it works, on the different devices. This is written by someone using KOReader primarily on a Kobo device and sometimes on an Android tablet.

Swiping down from the top of the screen gives you access to the menus. This is true both in the File Browser and in the Reader. The options available in the reader menu will depend of the type of file you are reading.

As installed, KOReader opens in the home directory of its "File Manager" , which initially is at /mnt/onboard/, fine.., if that is where your ebooks are kept, but there are good reasons to have them elsewhere, (especially for Kobo device users). So, the first thing to figure out is how to navigate the File Manager pages. (You might want to access the menus and tap the "Show hidden files" option, it should put a checkmark in front of the option.) Now you can look at all the file structure, but it will only show document or ebook files that KOReader can read.

In the file browser, you can tap on any file to open it. Long press on any file to bring up a menu with more options. The location path display above the list of files and folders shows you which folder you're viewing. The ../ entry, at the top of the listed folders, lets you go up one level. For instance, if you are at /mnt/onboard now, tapping the ../ will bring you to /mnt/.

At /mnt/ you should see onboard/, sd/, and user/. The sd/ is the external uSD card. Once you have found the folder you have your books listed in, you can long press the selection that opens that folder and you should see a message box popup with the option to Set as HOME directory.

KOReader lets you use a library structure of files of your choosing. You can make one all your own, or let calibre create one on your device. (Kobo users should note that any files that the stock software (Nickel) will process also files resident in a so-called "hidden" folder (".library" or ".books"). It is recommended to apply this patch. Calibre can use a folder as a device, including a hidden folder, and put its file structure there.

Having found or created a library of documents or ebooks, you can start reading.