Might be best if you ask this question within the Calibre forum.
As regards to removing DRM, best to use Google for that. Plenty of help available in that regard. Once you remove the DRM infestation, Calibre will take care of the rest for you.
In regards to using the Kobo with Calibre, I found it most straight forwards to use. Connect your Kobo via USB whilst Calibre is running and Calibre will automatically detect the connection and allow internal browsing of the books on the attached Kobo. You can then transfer books to the Kobo via Calibre. Once done you can eject the device and disconnect from the PC.
The Kobo will then process your newly added books and make them available for reading.