The main tools is Android SDK (software development kit). It contains libraries, debugger, documentation and tutorials, Android emulator and you can get it on http://developer.android.com/sdk/index.html
After downloading the Android SDK from http://developer.android.com/sdk/index.html, unzip the content into desired folder (e.g. /opt/android-sdk on Ubuntu or any other GNU/Linux distribution).
The ADT (or Android Development Tools) is an extension to the Eclipse IDE (Integrated Development Environment).
The ADT plugin has support for the creation and debugging of Android applications.
Here are some of the features you could use in Eclipse after installing the ADT:
An AVD is an emulator instance that enables you to model an actual device and it is used for running and testing your Android applications.
Each AVD consists of a hardware profile; a mapping to a system image; as well as emulated storage, such as a secure digital (SD) card. You can create as many AVDs as you want in order to test your applications with several different configurations. This testing is important to confirm the behavior of your application when it is run on different devices with varying capabilities.
I experienced the problem with my Ubuntu 12.04 installation a couple of days ago related to the updating process. The error message was:
Could not get lock /var/lib/apt/lists/lock - open (11: Resource temporarily unavailable)
If you have the same problem here are the steps that could solve the issue
utf8_unicode_ci is based on the Unicode standard for sorting. utf8_general_ci is very close, but is NOT Unicode compliant, because compromises have been made to make it faster. Despite it is a little bit slower we recommend using utf8_unicode_ci if your site need to handle non-enlish characters.