Here is an explanation:
sudo lets you execute a command as if you had logged into a different user account.
The -u option says which account, in this case the account is gdm
dbus-launch is the command that sudo is executing for you in the gdm account
gnome-control-center is a parameter you are giving to dbus-launch, it is another program that will be run (also in the gdm account).
All together, you type ONE command line just like this:
sudo -u gdm dbus-launch gnome-control-center
There is another issue: that gnome-control-center might not be able to access your X windows. In that case here is what I suggest:
a) log in as root
b) type xhost + (command xhost, argument +)
c) type the command line from above