If you buy a camera system with interchangeable lenses, you will have to deal with the question of which lenses to buy first. In former times, a single lens reflex (SLR) camera with a 50 mm lens was part of the beginner's equipment, thus a standard lens also called standard focal length. The focal length of such a lens corresponds approximately to the format diagonals, in the case of 35mm (today probably rather called full format, i.e. 24mm x 36mm sensor size) this is 43mm. A 50mm lens therefore has a slightly increased focal length. Focal lengths that correspond to the format diagonals have an image angle that roughly corresponds to natural vision. If you look with one eye through an SLR (SLR camera, full format) with a "normal lens" of 50mm at an object and at the same time with the other eye directly at the object, you will notice that this lens slightly enlarges the scene (this only applies if the viewfinder images the scene 1:1, which is rarely the case). The 43mm are almost exactly between 35mm and 50mm. This will probably also be one reason why the 35mm lens is also very popular and is used by many photographers as the standard focal length. In the past, not only 50 mm lenses were sold as standard focal lengths, some suppliers also supplied standard lenses with slightly larger or slightly smaller focal lengths. Today this has become rather rare, although there is a trend to offer lenses close to 50mm but not exactly 50mm. As an example the 40mm f/2.8 STM Pancake in the Canon EF system or the Tamron 45mm f1.8 VC could be mentioned.
As a beginner you didn't really have to worry much. The easiest way was to reach for the 50 (or similar) or to use a 35mm wide angle lens. The whole thing was a bit complicated (at least from the point of view of decision making) when zoom lenses were offered. The term zoom is actually misleading, as it refers to getting closer to an object with a constant focal length while filming. Therefore, lenses with variable focal lengths were called Vario lenses. However, this did not become generally accepted and today everyone only talks about zoom lenses; let's stick to this term. A standard zoom in the early years was a 35-70mm zoom, today it has changed to a 24-70mm or even 24-105mm zoom lens. Such a lens thus offers a large focal length range in one housing; it seems to be a clear case. Unfortunately, there are also other differences between a zoom and a fixed focal lengths. The latter often have a better image quality (let's not focus on this in this article), are much lighter and have a better opening (aperture). Of course, the point with the weight only applies to "moderate" aperture openings of fixed focal length lenses, i.e. 50mm f1.4 or 35mm f2.0. However, there are also some manufacturers who rely on much heavier lenses for fabulous imaging performance and consider the weight to be secondary. But let's stick with a 50 with f1.4 and typical 300g (example Canon EF 50mm f1.4). A comparable zoom has a maximum aperture of f4.0, i.e. 3 f-stops less (!) and weighs twice as much (e.g. Canon EF 24-70mm f4.0 IS USM), but a zoom with the same range but a better aperture will quickly triple the weight, i.e. about 900g. A heavy lens also shifts the centre of gravity of the camera-lens system. You'll soon notice that the camera is the main weight for a small fixed focal length and that the camera hangs very balanced on the straps. If you mount a heavy lens, however, the system will tilt forward. This is a lot more uncomfortable to carry, and of course it is also more difficult to handle because of the increased weight.
Despite all these points, zooms are very popular and many beginners start their photographer's life with such a lens. But a zoom increases the complexity of photography. You now have a new camera and you have to deal with all the features of the new device (and the manufacturers tend to put more and more functionality in one housing rather than less) and in addition there is the zoom lens. Now you also have the choice of focal length, besides ISO, aperture, time etc.. But a zoom also has the crucial disadvantage that it is difficult to train the eye for a certain focal length with such a flexible lens. If you have practised for a while with a fixed focal length, you will notice that the view is adjusted to the focal length used and you quickly notice which section you can reach; and that even without putting the camera against the eye. So you will automatically find an appropriate position to adjust the frame to the desired one. This "getting closer" or "getting more distant" really corresponds to the original concept of zooming (changing the distance to the object at a constant focal length). The nice thing is that the perspective of the image doesn't shift. If you only rotate the zoom ring, you will get the frame in one plane, but the perspective will inevitably change, i.e. the frame in the other planes will change differently than if you approach or move away from the object with a fixed focal length.
I also started to photograph over 30 years ago with a zoom. The desire for an even larger focal length range soon arose. The next step beside a standard zoom (e.g. 35-70mm) was a tele zoom (e.g. 75-300mm). Wide-angle zooms weren't that popular back then, so the next thing that followed was an extreme wide-angle lens (17mm) and a fish eye lens (15mm). Over time, these lenses were replaced by more powerful ones (i.e. 28-70 f2.8 and 70-200f 2.8) and then by higher quality ones (in the Canon system these are the parts with the red ring, i.e. "L" lenses). With the purchase of a Contax G2, a Hasselblad XPAN and later a Leica M8, however, fixed focal lengths were increasingly used again, simply because they were not or hardly available for rangefinder cameras. And so I quickly learned how comfortable such a small, handy lens is. Especially when you place a Canon AF zoom next to a Leica fixed focal length, you're amazed. And also the comparison of two fixed focal lengths from the two systems is very impressive. The same of course applies to lenses from any other camera manufacturer or third-party lens manufacturer. After this experience, I also decided on fixed focal lengths for the Canon system. First I started with three lenses: a 35mm f2.0, a 50mm f1.4 and a macro 100mm f2.8. This reduced equipment allowed me to use a small, handy photo bag. After a while I noticed that the 50mm lens was attached to the camera 90% of the time and finally I left the bag with the other two lenses at home more and more often. For about 2 years now I have been photographing almost always with only one focal length and I find this experience very positive. From time to time I switch to a 35 lens instead of a 50 lens. But the 50 is still the most used lens in my collection. Of course a 400mm lens is still used for animal photography and a 14mm or a fish eye lens for polar lights, but in photographic "everyday life" the 50 is my standard focal length. And the great thing about it is that you don't have to worry about photo bags anymore.