Unfortunately, if you want to strip DRM you'll have to learn to use the Terminal. You will find it in the Applications folder, in the Utilities sub-folder.
Make a Google search for mobidedrm. It's a Python script that you will need to execute from the Terminal in order to remove drm from mobi books, including Kindle books. But first, the hard part, for Kindle, is to get your device's PID, which is a unique identifier assigned to your Kindle and that you need to decrypt. I don't have a Kindle, so I can't help you with that, but again, Google and MobileRead should help.