The Arduino Companion is an Android app which has been designed to help anyone getting into Arduino and electronics. The app contains the full Arduino Reference for offline use, as well as a very useful resistor calculator.
As well as the standard Arduino reference you also get details of the included classes for controlling Ethernet, Servos, Serial Communication, LCD Displays, SD cards, Keyboard and Mouse (Leonardo) and more.
The latest version also covers the Arduino Due and has been updated to work on work on Android 4.4 and newer devices.
This app is one that I recommend you install, its very useful and importantly free. Its a 12m download and I have never had any issues with the app not working and thats on a couple of devices I own
full network access