New to Java

hi folks.

installed Java jdk 1.5.0
C:\Java\Jdk1.5.0\bin

q1)
on cmd command prompt, if i type jar, i get following error:
"Can't determine application home".

q2) I used JBuilder foundation to create a simple application with 5 classes.

Packge is called: sqlInsertion.

within the sqlInsertion i have the following directories:

bak, classes, src, doc.

I am struggling to use jar tool so thats my first concern. 2ndly I need to create an executable jar file, I have read sun's tutorial but i get following errors:

"Failed to load Main-Class Manifest attribute from " path ".jar". where path is the path to this .jar file I created.

Please, please help.