Fix the left menu and keep changing the right content

Hi, Can anyone tell me how to keep the left menu bar screen fixed and keep changing the right content area.
I have tried making a main.java file that makes the left menu and right content as desired but when i click the button on left menu, the whole page refreshes. I want only the right content to get refreshed. I have more than 20 views and all cannot be put in the menu buttons so have given links in the views that will be named in the menu .
Please help.
Thanks.
D.