To be able to read ebooks on Android, it is necessary to download an Ebook application in the Android Market under Android 1.5, Android 2.1, Android 2.2 or later; Several apps exist and not all are created equal. Here is a non-exhaustive selection of the best android ebook readers:
Aldiko Ebook Reader
It's the most beautiful graphically, but if you have a sluggish phone (like a Samsung galaxy Spica), it is not recommended to use it. It has a library of free ebooks because they have fallen into the public domain (example: ebooks by classical authors or Greek philosophers -> Sun Tzu, Freud, Apollinaire, Beaudelaire and many others). However, if you want to find more modern ebooks, you will have to get them on a specialized site and import them on your mobile.
Brightness is easily adjustable by sliding your finger along the left edge of the screen. It is also possible to return to the last pages viewed.
FBReader
This app does exactly what is asked of it. It reads books, it has a library and allows you to go back to where you stopped reading and has several anchor points, such as the last chapters read. It has all the advantages of Aldiko mentioned above except that its interface is a little less aesthetic. Its use is simple and intuitive.
It is recommended for any type of Android phone because it does not consume much resources. A library of classic books that have fallen into the public domain is also available. Like Aldiko, you will be able to import ebooks stored on your internal memory card or MicroSD (EPUB format).