With a zoom lens, you can change the focal length to zoom in or out (there’s a proper name for it but it escapes me). With a prime lens, it’s fixed – no zoom. Because prime lenses are fixed, they can offer lower apertures and often far superior quality but mean you need multiple lenses to cater for different situations (and therefore means more lens changing). With zoom lenses, you don’t need to switch it as often but you loose out with quality and a generally higher minimum aperture. The great thing with being able to use a lower aperture is that you get better low-light photos (but in turn less depth of field). You’d use a prime lens in the same situation you’d use a zoom.. You’d just use them differently and get slightly different results. I think Pros only use prime lenses.