It’s been awhile since I did this but I believe you go to the Google Play Books Partner link here. Google Play Books Partner Center. You will be guided through a setup as a partner. You have to set up an account. There is an approval process. You have to give them information on how to pay you. Eventually you will have access to the Partner Center Dashboard. There you can add your books and track sales and so on. T give lots of information and help.
The next best way is through the B&N network. There’s a few different ways of going about it If you are on iBooks there are some services out there which will not only do the hard work and deliver your book over to B&N, but they will do it in such a way that you don't ever actually have to pay B&N anything. Here is one of t barn owls_ on B&N BarnsFlats and another that I have tested myself on and are both quite awesome. BarnsFlats : How to do a hard drive-to-drive transfer? pic.twitter.com/KkNx4v5J6D — Michael P. (Michaelmas) May 3, 2014 For B&N and Barnes & Noble on the other hand it's more of a hassle and t here are two options. For Barnes and Noble they have a nifty little interface called “Oppress” which allows you to run a simple command to drop your .pub onto their Kindle.