If your prompt starts with a $ then you will need to precede the command with sudo.
Start
# /etc/init.d/apache2 start
or
$ sudo /etc/init.d/apache2 start
Stop
# /etc/init.d/apache2 stop
or
$ sudo /etc/init.d/apache2 stop
Restart
# /etc/init.d/apache2 restart
or
$ sudo /etc/init.d/apache2 restart