The commands are correct
Start a terminal (/Applications/Utilities/Terrminal.app) and at the prompt type:
sudo periodic daily
you will be asked for your administrator password (this happens whenever you try to 'sudo' anything...it's checking to see if you have administrator privileges). Enter your password.
You can also type
sudo periodic weekly
and
sudo periodic monthly
Any of these may take some time to execute, depending on how big your drive is, and how long it's been since they were last run.
If you leave your system running, these scripts will get run automagically by the chron system. However, if you shut your system down, or it goes to sleep when you're not using it, they may not get executed, and rubbish will accumulate on your disk, degrading performance and using up space.
Something else that you should do periodically is to repair permissions on your boot disk. To do that, start diskutility (/Applications/Utilities/diskutility.app), select your boot disk, and open the first aid tab, and press the 'repair disk permissions' button. This process will also take some time to complete, but you can continue to use your system while it runs.
I've found a few irritating little problems have evaporated as a result of running 'repair privileges', but I've never really noticed any problems go away after running the periodic scripts. But running them can't hurt (if you want to see what they do, the actual scripts run by the daily, weekly and monthly commands are in /etc/periodic).
I think you'll find that the maintenance requirements of your Mac are considerably less onerous than your PC, and there is also much less superstitious behaviour associated with running a Mac (on my PC, I used to reboot whenever anything went wrong, and that often fixed the problem, but I never knew why...I haven't rebooted my Mac for months).
Cheers
