Jar files don't exactly work that way... First, you can't just place class files anywhere. They have to be placed based on package. Second, you can't just place the manifest in the root. They should be placed in the directory reserved for manifests. And third, I don't think that you are allowed to place jar files in jar files.
Once placed correctly, you can specify the main by a field in the manifest. You can also specify the classpath to use, to locate the other jars, by another field in the manifest.