JAR & JAD files

JAD file
This file doesn't contain the contents of your program(source code etc). It actually links to the JAR file. JAD file is used when downloading applications using Over-the-air(OTA) or when you are signing your application.

JAR file
This file contains all of the contents such as source codes or images. You can normally unzip the file and see all of the contents inside.

Installing applications to phone
You can normally just copy the jar file and paste it inside your hp. Either by bluetooth or cable. Or if there's a memory card, just paste into the memory card. However, if you wish to use the jad file too, you must ensure the jad file and the jar file is pasted together. Without the jar file, the application can't run with a ClassNotFoundException.