Hi Phil
Welcome along.
Although Ian has answered pretty much everything, there is one other way of shooting macro. On top of the macro "adaptors" (the screw in magnifiers), extension tubes or a macro lens you could also buy something called a reversing ring.
This allows you to mount a lens backwards onto your camera body. For this to work properly you're going to need a lens with a manually selectable aperture and the G series of Nikon lenses don't have this - you control the aperture using the controls on the camera body. However, the lens doesn't have to be a Nikon fit lens (as you'd mount it backwards) so you can pick them up for a fwe pounds on eBay etc.
It's not the easiest way but it will give you the best quality results for minimal cash outlay. Of course, with a reversed lens you have no metering so you have to start guessing at shutter speeds but you just keep trying until you get a correctly exposed shot.
The principle of reversing the lens is this... If you think that the rear elements of the lens normally poke into the camera body and focus light onto the sensor which is very close to the back of the lens. Turning the lens around and using the rear end of the lens means you
have to be very close to the object you're photographing.
I've only just started with macro photography and this is how I've been doing it because you're still using a "proper" photographic lens rather than putting the close-up filters on (which might dedgrade image quality), it's much cheaper than extension tubes and even cheaper than a proper macro lens. I've posted a couple of example images below which I took with a reversed Nikon 35mm f/1.8
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