Canon 90d belongs to Canon's semi-apsc framework. From the processor, pixels, control, size, battery and other aspects, it is a relatively high-end half-frame fuselage.
Because it is a half-frame fuselage, there is a cutting factor of 1.6 on the lens, that is to say, the actual visual range = lens focal length × 1.6, and a similar 50mm lens (whether ef or efs) is placed on the half-frame fuselage, the focal length becomes 50× 1.6.
Other suggestions:
You can start with the standard zoom lens 18-55, 18- 135 or 18-200. They basically include wide-angle end, medium-focus section and even long-focus end. In this way, it is more convenient for daily use.
If you set the focus, you can give priority to Canon's 50 settings, and the large aperture of 1.8 is not expensive, which is very suitable for beginners to shoot large apertures and night scenes. If you often sweep the street, you can also match a 35-episode documentary lens, which belongs to the humanities lens and can also take into account the scenery shooting.
As for the original factory (Canon's own lens) or the branch factory (other manufacturers' lenses, such as Longteng Yima), the original factory should be given priority when the capital budget is sufficient. On the one hand, the quality of the original lens is good, on the other hand, the original singing lens generally has anti-shake and Canon's body does not. However, Sigma has some lenses such as 35 1.8, 18-35 1.8, which is very suitable for half the fuselage.