Can someone give me a concise way to make JAR file?

I read through Sun's steps to make the JAR file, but i can never execute the file using the "java -jar filename" command. I always get a "Main Class not found" error. I have JRE 1.3.1.

The file structure is kind of weird. All the class files are in a package called PHYSICS. Do i have to create my own manifest? when i was reading Sun's documentation on creating Jar files it seemed like manifest files are created automatically.

So can someone give me a basic step by step way to do this? the files are:

C:\PhysicsApp\file1.class

C:\PhysicsApp\file2.class

C:\PhysicsApp\file3.class

Thanks.

[643 byte] By [rpk5928] at [2007-9-26 2:09:30]