I am trying to make my girlfriend an app for her Droid, and all I can do is program in Java. So, I have a executable .jar and so how do I get it working on her phone? Does it have to be converted? Or can you just apply it straight to the phone? If so how?
No, it won't run as is - you need to use the SDK tools to convert all classes/jar files into an Android-compatible format. But more importantly, the Android API is rather different from desktop Java, e.g. the java.awt.* and javax.swing.* packages are not available - Android has its own, rather different, GUI technology.
If you haven't done so yet, download the Android SDK and look through its documentation (also available online at http://developer.android.com/guide/) - it contains many introductory articles on the API and the tools you need to use. The AndroidFaq also points to much useful material.