I use LibPRS and think it is relatively straightforward (I hope) if you understand the process. Note that when we say "book" we really mean just about any document. Images usually get stripped out because the current technology does not display them very well. But apart form that "book" means web pages, Word files (saved as rich text (rtf)), ebooks bought online and so on. Once you have installed LibPRS and started the program the steps are:
- import your books and documents
- convert them to "lrf" format
- send them to your lissoose
Importing can be as simple as dragging and dropping the files into the LibPrs program, or you can use the "Add books" button and browse for files.
Then select the new files and hit the "Convert E-books" button (if you have more than one it's probably better to use the drop-down arrow next to that button and go "bulk convert". It's best initially to just hit "ok" on the dialog that pops up asking you to customise the conversion.
Now wait until the hourglass stops going round.
Once that happens all your books are converted and it's time to hit the "send to device" button.
That's it. Unplug your lissoose and it will display the rotating arrow "wait" icon for a little, and when it finishes you should have a bunch of new books on your device.
The official user manual here:
http://libprs500.kovidgoyal.net/user_manual/ does help but is written for people more geeky than average I fear.
Edit: I haven't actually tried any of the Microsoft-format books, directly. I have some but when I got them I immediately converted them to HTML and have not touched the originals since. ConvertLit is probably the program you need for that.