If you are new to Android it is good to know that there are some default icons in Android you can use in your own applications.

There are two ways you can use them in your application:

1. You can use them in your code or in your XML layouts using android.R.drawable class.
2. You can make local copies of standard Android resources and use them in your projects

Example of using android resources with android.R.drawabale class

or in XML layout:

If you want to make local copy of any resource go to folder where Android SDK is installed. On my system it is C:\Program Files\Android\android-sdk. Here you will se \platforms subfolder which contain one subfolder for each anroid platform version (\android-3, \android-4, \android-7, etc). Each android platform versions folder contain \data\res subfolder from which you can make local copy of resources.

According to Android Icon Design Guidelines it is better to make local copy of resources because resources can change between platform version. In that way you can maintain control over the appearance of your icons, even if the system's copy changes

Here are some useful pages where you can see default android icons and its resource identifiers.

http://since2006.com/android/2.1-drawables.php
http://www.darshancomputing.com/android/1.5-drawables.html
http://developer.android.com/reference/android/R.drawable.html