Camera Labs

With macro-lenses you don't zoom closer you just focus closer.
As a rule of thumb: if f is the focal length (say 60mm) then you can shoot an object at 2xf (in this case 120mm) from the front lens to get 1:1 magnification.
This also tells you the major difference between a 90mm and a 60mm macro lens: With the 90mm macro you can keep a larger distance to your subject which might be convenient or simply practical.

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Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews, My Pictures, My Photography Blog
D800+assorted lenses

Thanks Thomas. So I understand somewhat of what you trying to say. Yes, I agree that more the focal length, more further back (away) I can get from subject. This is true, but what if I can't shoot from distance. For example, last year I went to Botanical Garden in Chicago, which obviously had many different types of flowers. And as expected place was crowded and everybody trying to get their best macro shot. So in such situation, I really dont stand chance to click a tiny flower from long distance. So will I be able to use 60mm or 90mm to stand in very close to flower and take macro photo with 1:1 magnification? Since I never got chance to use any macro lens, so am little struggling to understand how does these lens works on DSLR exactly. With my previous point and shoot camera (Canon S5 IS) I could easily go as closer as 6cm from subject and take a macro photo. So I am only trying to understand whether I will be able to take macro photo from 18.5cm which closest focus distance for Nikkor's 60mm lens.

The shorter the focal length, the closer you have to get to your subject to get a great magnification. So the micro Nikkor 60mm is the lens where you really can (and need to) get up close and personal.
And by the way, the lens is a great performer, as you can read here.

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Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews, My Pictures, My Photography Blog
D800+assorted lenses