File does not exist: /var/www/polls
If polls is the name of the app within the example project, your example.conf file should probably have this line:
<Directory /var/www/example/polls>instead of this one:
<Directory /var/www/polls>
Thanx for trying to help. I have sort out the issue. Everything was correct. The conf file that i have created was not enabled. So I ran the following command.
a2ensite example.conf