Since your question isn't in any way related to Swing / AWT / SWT, I've moved it to a more general section of the Ranch. Also, please go through the sections on "Use A Meaningful Subject Line" and "Use Code Tags" in How To Ask Questions On Java Ranch
Do you know how to find the Java API? Go through the documentation for Class#forName(...) and if you still don't understand, tell us what is confusing about it.
There are no new questions, but there may be new answers.
bala, I see you didn't return to all but one of the threads you started. When other members spend their time to help you, they like to know whether the help offered was useful or not, and whether your question is answered adequately.
There's a section in the page I linked to titled SayThanks <- link Please go through that one too, or maybe just go through all the sections.
I won't cover the general use of Class.forName(). In this case, the call to Class.forName() will cause the specified java class to be loaded and its static code to be executed. This static code will register the database driver under the name "jdbcdbc:lib" in the JDBC driver list, thus allowing you to use it to open a connection in the following line.