Difference between raster images and vector graphics
Computers use two kind of graphics which are raster images (bitmap images) and vector graphics in our daily lives. Each one has specialities for it's own kind and can be used for the needs.
Rasters are the images commonly called as bitmap images. Bitmap images are consisting of pixel grids where each one represents a different color code or color shade. After the beautiful connection of all pixels represents a color code, we are able to see an image.
Vector graphics are working with mathematical relations between each point and path, when they are connected we can see the image. Vector graphics are life saver for designers if they aim to change specific color on the image, not to lose resolution when changing the size of an image and many more other usefull benefits.
Most common difference between a raster image and a vector graphic is scaling. You can resize (scale) a vector graphic without loosing it's resolution because vector graphics are mathematically built with points and paths. You can scale a vector graphic to 400% and can see the image is still smooth as in the begining.
We prefer vector graphics for printing to get the highest quality. The most important issue is, changing the extension of a jpeg or png file to pdf is not re-building that image as a vector. Vector graphics are made with softwares like Adobe Illustrator, CorelDraw and etc.. Best printing quality is made with vector graphics but we try to serve our customers the same quality if they don't have a vector graphic.