A zoom lens is a mechanical assembly of lens elements for which the focal length (and thus angle of view) can be varied, as opposed to a fixed focal length (FFL) lens (see prime lens).”
A simplified zoom lens works by combining two parts: a focusing lens similar to your standard prime or fixed lenses and a focal zoom system, which is the sliding element that does not focus on light. Rather, it focuses on altering (thus magnifying) the size of the light. What’s important is that, while the zoom comes from this sliding lens, it is necessary to compensate for any movement of the focal plane to keep the focused image sharp — which means either you have to physically move the camera or move the focal plane to compensate.
I personally dislike zoom lenses as I have a better quality image as the lens is designed for a single focal lens thus not a compromise and I have more control over bokeh, subject separation etc with a prime due to its fixed length and lower f stop.