So let me guess, you haven't had any experience with ebooks? That's ok we all have to start sometime.
I'm not one to answer directly about this site. Hopefully others can help with that. I'm sort of new here myself.
You might try Tuebl.com for books as well as places like Barnes and Noble, Kobo, Sony and the like and be sure to check back here because I'm sure others can give you hints. Some books you pay for and some are free. The site will tell you the policy and Kobo and the like will have the price with the book. You can also ask your local library if they have ebooks. They lend them for a period of time like checking out a book from them. I belong to my local and to the Philadelphia Free Library. In my case the Philadelphia Free Library is free for me even if I don't live in Philadelphia because I am a Vet. If I wasn't I either have to have an access sticker from my local library or pay $35 to join.
To read you want an ereader. This can be something like a Nook which is portable and you carry it with you. Or you can use something like Calibre. You install calibre on your computer and read from there. Depending on your device [ereader that stands alone] you can either transfer directly to the device or download it then install it on your device from your computer.
And there will be a lot more questions but this should help you get started.