Hmmm....Ok. A Vector layer makes a picture by registering points and connecting them. A Raster Layer makes a picture by creating a grid of points.

A better way of thinking about it is like a photo. A vector layer makes the picture like it is in a higher definition. As you increase the size, the photo loses none of it's clairty. A Vector Layer creates an image that is made of a few pixels and doesn't size well. As it increases in size, it becomes more and more jagged on the edges.

(I had to look that up! Basically Vector Layers are better for images like pictures, Raster Layers are better for lines and painting. )