When light shines through a piece of glass the rays refract (bend) because the speed has been altered. If the glass is shaped in different ways, then the image that results can appear larger, smaller, closer, or farther away.
A concave lens is shaped so that it is thicker at the middle point than on the ends. Like the front of a spoon. The image formed by a concave lens depends on where the object is relative to the focal point. For example, if the object is a longer distance away, then the image will appear to be upside down. If it is closer, then it remains upright and gets smaller as the object moves closer.
Convex lenses are shaped like the back part of the spoon. It has a reflective quality that causes light rays to disperse and spread apart. This gives more view of an area. Rearview mirrors and side view mirrors on cars are good examples of this. Also, convenient stores use these large mirrors to get a good view of customers in the back part of the store.