It should have either a push or a slide one,
but we'll move on then,
plug the kindle into your computer via usb cable
then sign in to your amazon account on the computer, and go here: http://amzn.to/2bO5NDP
Choose a book you want to download, click the box next to it and click actions, then download and deliver to, choose your kindle,
then watch for the saved/downloaded book file.
Open your computer/explorer/finder folder, and on the left column you should see the kindle "drive" appear, open that up and then find your downloaded book file, drag/drop or copy/paste it to the Documents folder within the kindle drive.
When you disconnect the kindle, the book should be in your library.