Creating the jar file

[system.drawing]

My java app is put in the folder with structure as below ...

\myapp
\myapp\myapp.class
\myapp\libs
\myapp\libs\lib
\myapp\libs\lib\lib1.class
\myapp\libs\lib\lib2.class
\myapp\libs\util
\myapp\libs\util\util1.class

My question is, how do I create the jar file from the application above ?