how does a zoom macro lens work?

What's the difference between a 35-105 macro zoom lens, and a 35-105 zoom lens? (For example, I'm looking at the canon 35-105 F3.5 macro FD (72) / 2 touch. For that matter, I have no idea what the "(72)" or the "/2 touch" mean.

I keep searching google for a basic site that explains details like this (and the basics of how a zoom lens works) but haven't found one yet. Any links would be much appreciated. TIA

Okay, all at once here.

A zoom macro refers to how close you can actually focus. 'Macro' is a very loosely used term, and has no firm meaning. Instead, look to see what kind of magnification ratio the lens achieves, usually expressed as "1:4" or "1:2". Treat this as a fraction (1/4 or 1/2) to get how close the image will be to lifesize on the film itself. Obviously, the closer you can get to 1:1, the better, but most zoom macros don't get near this.

The 72 refers to the filter diameter, basically the size of the front element. 72 is pretty big - gets expensive in filters, but may also mean it lets in a lot of light, which is very useful.

One-touch and two-touch are the method of zooming and focusing. Two- touch means you have a separate ring or grip for zooming than for focusing.
One-touch means it's the same grip - slide it forward or back for zooming, rotate it for focus.

Other terms you may run into:

Constant-focus and vari-focus - constant focus means the focus point will not change as you change zoom settings. Vari-focus means if you change the focal length (zoom), you have to refocus.

Internal-focus or rear-focus - Close to the same thing. Means the front of the lens does not rotate when you change focus. Useful if you do a lot of filtering, because the filter can rotate as you tweak focus otherwise, which messes with polarizers, graduated filters, etc.

Many current zooms, especially the lower-end ones, also change their overall length when you zoom. Not too much of a hassle, but sometimes tricky with macro work (the lens can start interfering with the subject or the light thereon) and often subject to 'zoom creep', meaning the focal length can change from gravity if the lens is pointed up (sky or treetop shots) or down (hanging from your neckstrap).

Most zooms with a fixed maximum f-stop (like you list above, instead of saying something like "4.5-5.6" are internal- or rear-focusing, and do not change length when zooming. Probably see this a lot more often with FD lenses than with consumer zooms nowadays.

Hope this helps. Good luck!