Hi Ghiraunla,
if you username is the ghiraula that grows over the roof in Nepal, I am not that big fan of it so can't help you out.. JK ;)
What I meant of simple costumer management service application is, try writing one application with a simple jsp/js/html which takes first name, last name, costumer id..
write some java classes to handle these, deploy them in server, connect to database and store them in the database (and vice-versa). Here are the tools you need to start with.
1.eclipse
2.tomcat
3.SQL developer
4.JDK (you probably have one already)

If you are completely new to development environment, they might look scary to you. (believe me they are not)
PM me with your email/phone if you have any questions, I will try guiding you as much as I can.