Hi,
I'll make an attempt to answer some of your questions although I will admit I'm not real familiar with that particular housing and camera. A slave strobe fires from a signal from another strobe. In other words, it will go off after another strobe, or the camera's flash, goes off. This is one way, but not the only way, to make a strobe fire.
- Why do I need fibre optics?
Fiber optics is one way of making the strobe fire without it being hard wired to the housing/camera. It is less prone to failure (e.g. flooding) than using a hard wired electrical connection.
- Does a strobe give you the nice glossy prints you see in magazines?
That is a hard question to answer! I would say "sometimes". But getting nice glossy prints requires so much more than just using a strobe. There are many, many things that go into making "nice glossy prints you see in magazines". Your chance of producing a print like you see in a magazine is MORE LIKELY achieved when using a strobe (or two strobes, as many are shot using two strobes) but it is not absolutely essential.
To attach a strobe to my DC34 case, what things would I need exactly? Arm? Cable?
I'll leave that one to others more familiar with that setup.
- I read something about changing aperture to match distance etc...
Hmm, I'm going to guess you are referring to what's known as "depth of field" though I could be wrong. Could you be more specific?
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Does the camera sychronise with the strobe or do you have to start being very smart with the way you take photographs
All I can say is that if you have to be very smart with the way you take photographs, I would not be able to take any photographs 
But seriously the camera connects with the strobe usually by either a hard wired electrical connection (e.g. cables) or by fiber optic connection. As mentioned earlier, they can also be fired in slave mode.
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I am not familiar with the strobe you mention but perhaps someone else here will jump in with some information.
I recommend that you get the book The Underwater Photographer by Martin Edge. The Third Edition has been out for some time but the Fourth Edition has just come out and I understand it is shipping now.
Also, you might want to give Reef Photo and Video a call. They are one of the sponsors of this site and they can provide answers to all of you questions. They are a great source of information and many on this forum use them for all their underwater needs.
Above all, feel free to ask additional questions as they come up.
Cheers,
Ellen
