In order open api demo in your eclipse File>new>Android Project
From that 'New Android Project' window, you select Create Project from existing sample
When you select your target, you can select 'Api-demo' from the
samples list
This will open the complete api demo in your eclipse and when you run this project in
device you will get it in device also. you can edit and use it as you wish.
new :
In Eclipse Android plugin (ADT) there is a wizard for creating the sample projects.
In eclipse Go to:File -> New -> Other ... -> type Android into search box -> Android Sample Project -> Next -> select your api level -> Select any of the samples, for example ApiDemos
Project called ApiDemos is created
Right click on it and select Run As -> Android Application