I'm also very new to flash. In fact, just treated myself to an SB900 at Focus on Sunday.
However, the other half bought a
Nissin Di622 which is only £100 and is a better specified gun (I think) than the Metz and it's cheaper than the SB600. We've been playing with that the past couple of days and it's great, highly recommended.
With my Nikon kit (hers is all Canon - pah!), I've had no trouble at all with my D90 and SB900 using CLS. I don't know how it would work with an SB600 but it's a piece of cake with the 900.
As Steve said, it triggers the strobe via the cameras own pop-up flash but you can "mute" it so that it only triggers the main strobe and doesn't flash into the exposure itself.
On the D90 all you need to do is go to the custom menu "e2" (Flash cntrl for built in flash) and change it from TTL to Commander. Commander mode allows you to then set groups of flashes (of no relevance if you've only got one strobe) and the channels.
If you set the built in flash to "--" it won't fire but it will trigger the external CLS connected flash. As I've only got the one flash I'm using group A (wouldn't matter though) and channel 1 and I've set group A to TTL so that the camera controls everything for me.
The idea is that you can set several flashes in each group and have each group firing differently.
If you're not in the mood for CLS there are loads of wireless triggers out there. Pocket Wizards are usually considered the best ones going - you'll pay for it though. Alien Bees are also very good but also expensive.
All is not lost though because, along with the Nissin Di622, the other half also got an
Interfit Strobies iSync 4 which is a bargain at £45 and will trigger flashes using IR or radio. Extra receivers are about £30 so you can expand the system quite easily as well.