These are books you can download to your phone or tablet. Most of them are free, but donations are appreciated considering that there are hundreds (if not thousands) of hours that have gone into producing them.
You can distribute these freely to friends. Each one comes as either a PDF or an .epub or .mobi document which are formatted for smaller devices (phones and tablets). You may need to download an ebook reader from Play Store or Apple Store, depending on your device type.