I agree – if you’re going to invest in a camera, particularly one with interchangeable lenses, take the time to learn enough that you can make an informed decision. Otherwise it is very easy to throw away a lot of money buying equipment that doesn’t work for you or meet your needs.
I’m sure there are beginners’ guides to photography on youtube or whereever that can provide a more systematic introduction, but here are a few notes based on my own crash course in camera technology over the last few months.
Focal length (the 55mm, 100mm, etc. that people use when talking about lenses) essentially describes the angle of view provided by a lens. What that means practically is how much you can focus in to capture only a particular section of a scene. A short focal length will be quite wide, whereas a long focal length will be quite narrow.
The focal length of a lens does not directly determine its working distance – i.e., how close you can get to your subject and still be able to focus. While optics play a role, it is also a matter of lens design: two lenses with the same focal length may have different minimum focus distances.
There are of course some general tendencies: long telephoto lenses are likely to have a longer minimum focus distance than shorter lenses. Again, this is partly due to the fact that such lenese are meant for photographing distant subjects and thus they are optimized for this rather than for close-ups of flowers.
Macro lenses, by contrast, generally have quite short working distances, often just a few centimeters from the end of the lens. This is an effect of the optics needed to achieve the high magnification. When people talk about macro lenses that offer longer working distances, “long” is quite relative; they aren’t talking about half a meter. A gain of even a few centimeters can make a difference in whether your subject flies away or not.
The focal length also does not determine the maximum magnification – i.e., how large the subject appears on the sensor. This is where macro lenses come in. But magnification is not equal to detail, and you don’t necessarily need to have 1:1 magnification in order to capture fine details. The amount of detail in a photo also depends on things like the resolution of the camera, quality of the lens, accuracy of focus, etc. For many purposes, even something like a 1:5 magnification which many non-macro lenses can manage may be quite sufficient. I’ve gotten photos that show the individual hairs and antenna structure on (largish) bees using the standard zoom lens that was sold with my camera, though this doesn’t compare with what my macro lens can do.
Another thing to be aware of is depth of field. This refers to how much area (depth) of the image is in focus at the same time – i.e., if you are photographing a bird in a tree, the bird and the branch it is sitting on will be in focus, but generally anything that is signficantly closer or further away will be blurry to a certain degree. Normal lenses generally have a depth of field that is sufficient for capturing medium-to-large subjects (pets, people, vehicles, etc.) without rendering the tail end of the subject as an unrecognizable blur.
However, with macro lenses, the depth of field is typically measured in millimeters or even fractions of millimeters. There are various techniques to compensate for this, but what it means in practice is that macro lenses are good at doing things like photographing small subjects or details like the hairs on the leaves of a plant, but it can be challenging use them to get a photograph of the overall plant (say, an average-sized wildflower) because when you focus on the flowers, the leaves and stem are a blur, and vice versa.
Does your mom have multiple lenses for her Nikon? If you are struggling to get a sense of the terminology and how it translates in practice, it might make sense to go out with a few different lenses and just “play” with the camera – experiment to see how the lenses behave, what happens when you change settings or focus on something close vs. far away, etc.
Also, one way to get more magnification (and, as a side-effect, a shorter working distance) with an existing lens is to use an adapter which clips or screws on to the end of the lens. A popular option here is the models made by Raynox, which you’ll find plenty of discussion of in the forum. Since you have access to a camera with a telephoto lens, something like this might well be a good, inexpensive option to try out close-up photography before investing in a major purchase like a macro lens. If flexibility is something you value, one advantage to such a set-up is that you can quickly switch between macro and distant subjects like birds without having to change lenses.