You can use the Android library to create applications based on the Box Rest API. You can find documentation for the Rest API at http://developers.box.net/.
Javadocs for the library can be found in the gh-pages branch, or by going to http://box.github.com/box-android-sdk/javadoc/
You must first obtain an API key by registering your Box.net application.
A sample app has been included to demonstrate usage of the library. In order for the sample application to work, you must set your OpenBox app's API key into BoxAndroidLibrarySample/src/com/box/androidlib/sample/Constants.java.
The Box Android library requires mime4j, httpmime and gson. If you do not already have those included in your project, you will need to include them.
mime4j: http://james.apache.org/mime4j/index.html
httpmime: http://hc.apache.org/httpcomponents-client-ga/httpmime/index.html