You just drag and drop the mobi file into the documents folder on the Kindle. If you are on macOS, you need the Amazon USB File Manager app to do that on newer

You just drag and drop the mobi file into the documents folder on the Kindle. If you are on macOS, you need the Amazon USB File Manager app to do that on newer MTP based Kindles. Older kindles just used ordinary USB mass storage protocol. Link in readme.