The way that you can listen to them free is to go to one of the above websites. You can listen to free books on audible. Audible Channels is a free feature for Amazon Prime members.
There is a way to listen to them for free without a membership at some sites. People can get these books at app stores. There are about 11 websites that have them for free online.
Project Gutenberg has a large library of computer generated and human-read audiobooks for people to hear.
There are about 5 different ways you can listen to this type of material.