I publish through both CreateSpace and KDP Direct, which are the print and Kindle publishing arms of Amazon.
On both platforms, you are only allowed to publish work to which you hold the copyright. Generally, that means your own original work.
If you're publishing something that's entirely text, all you need is the text, properly formatted, in Word, and a cover image. There's plenty of help documentation available to publishers, to help them get their work formatted correctly, and the online tools make it very simple to go from Word document to finished book. The easiest way to publish in both print and Kindle is to go through CreateSpace for print, and then allow them to export your cover and interior over to KDP Direct.
If you're publishing something with images, or that's entirely images with a little text, you'll need something more robust than Word. I use Publisher to layout my print books, and Kindle Textbook Creator to convert them to Kindle, while keeping the layout intact.