1. First of all, iTunes is a must. After entering the App Store, you will see a book label at the top. After entering, you can download it like other applications, but the resources seem to be in foreign languages.

2.2. The file formats supported by iBooks are pdf and epub, but there are few epub resources on the Internet. If you have a MAC computer, Pages (equivalent to PC WORD with the save as epub option) is a good software for making epub format. Of course, epubbuilder on PC can also convert files in txt and other formats into epub. If you think it is troublesome to make your own books, you can only download e-books made by others online.