Well, you can use the command line or you can use a button...

The command line is:
sudo shutdown -P now

or

sudo reboot

The first will totally power down, the next should reboot you.

However, if you have a gnome panel up and going, you should be able to
right click on the panel and choose "Add to Panel..."

Then select the item titled "Quit..."

Once that is added to the bar, it will allow you the same access to the
shutdown, logoff, restart, hibernate, and suspend scripts as well as
lock screen and such that you are used to.