Welcome to MobileRead.
This is the Introductions forum, our usual help monkeys reside in the Calibre forums here:
https://www.mobileread.com/forums/forumdisplay.php?f=166 -- you are more likely to get answers if they can see your posts. In the future, it is probably better to post calibre questions there.
You can add books from the Kindle by plugging your Kindle into the computer while calibre is running, and you will see a "Device" toolbar icon, with a list of books on your device. Right-click on a book or a highlighted group of books, and you can select "Add to library".
Many books will have DRM, which makes them unreadable except by that device. For more details, and what you can do about it, see
http://apprenticealf.wordpress.com