Android is a mobile operating system running on the Linux kernel.
Hello World App
How the Hello World App looks on your computer while running.
Read more of how to fix the initial problems with Hello World App.
Test application on Phone
Install applications on your device (a k a Phone) using USB-cable. First you need
to set your application project flag
Second you need to run the application on Eclipse while device is connected
(and mounted) on your computer. Application installs itself on your device in debug-mode.
Be sure to turn your device to debugging mode:
Application settings > Development > USB Debugging.
Fun isn't it :)
Ref: Setting up a Device for Development.