Let's just be clear. This isn't an argument for Primes and against zooms. This is a starting point for a beginner who wants to start taking excellent images and I feel the 50 F1.8 as a great starting point for beginners who don't want to invest thousands of dollars in thier first lens but still want something with excellent image quality.
Zoom lenses are great and I have several. Truth is I shoot with both and there are plenty of reasons that you don't require explainations for but I will give a few.
A wide angle zoom lens won't ever be able to go down to F1.4 or F1.8. If you shoot people then you want a thin focus plane to isolate the subject.
I also never expect beginners to shoot on a tripod. For one it's another expensive piece of equipment and another people don't want to walk around with one. I prefer using Aperture vs using ISO in low light due to image quality. Dave and I differ on this point and that's ok. We both do what works best for us.
I use Aperture for effect. If I shoot something where I want the background out of focus I will shoot the lens "wide open". That's to say a lens with its Aperture as wide open as it will go (small F#).
Shooting a lens "wide open" as I say makes for a pleasing background. If you want to be creative with your images then Aperture is one way to do it. The out of focus area can provide some interesting backgrounds. We call it "Bokeh" you will hear that word a lot in certain circles.
The blurred out area is refered to as Bokeh. Some lenses provide a pleasing Bokeh. An example of being creative using Bokeh is say at Christmas time with the lights. Having the lights out of focus behind your subject makes for colorful circles that add effect and make an image more pleasing to the viewer.
The only way to pull that off in camera is with Aperture and the larger the Aperture the greater the effect. To a degree you can accomplish this with a zoom as well but mostly with the telephoto zooms that have large Apertures and a fair distance between the subject and it's background. The large Aperture primes are what most people rely on for this effect though.
This was taken with my 50 F1.8. Notice the lights behind the car out of focus.
Bokeh GT500 by -mik3ymomo-
Same with this shot. Taken with the 50 F1.8. The lights and bridge out of focus behind it. I wish I had a 50 F1.4 or even a 50 F1.2 for this shot to add even more effect. Hopefully you now understand the effect of a large Aperture shot wide open as it pertains to depth of field, blur/Bokeh.
Steves67 by -mik3ymomo-