What's the difference between 18-55 mm lens and a 50mm lens 1.8?

I'm getting a DSLR (Nikon D3200) and I need a good lens- the camera will mostly be used for grasping moments of my daughter growing up

In general, lenses perform best at least 2 stops from max aperture. That means for a 50/1.8, it's probably sharpest between f4-8. For a 18-55 zoom which probably has 3.5-4.5/5.6. It's sharpest aperture is probably between f8-11. But that's only if you push them to the limit. For general purposes, what matters the most is the focal length and max aperture. As a 1st lens, just get the 18-55. 50/1.8G is more specialize for portrait or indoor where it does really well, but kind of limited if it is your only lens.