i want to learn android op.sys. by myself only.so pls suggest me any online free ebook which is so simple and used for primary users.

Head on over to IT Ebooks and have a look around. They've got plenty of free books on a range of IT topics and languages.

Many android operating system books are available on the internet and it is very useful for your study.I will share some details.

Android (Operating System) - Unabridged Guide
Android OS: The Unofficial Handbook
Learning Android