Another terrible example of use of on-camera flash. This is even worse when compared with the last one. Modern DSLRs have TTL (through the lens) metering which would prevent overexposure of foreground subjects such as in this. But in general it's terrible to use on-camera flash as the only source of light.
Instead, think of your flash as a light source, as a compliment to your environment and as a balancing tool to light your subjects. The Strobist is the ultimate source of information on learning how to use camera flashes. For technical details of Canon flash systems I recommend the photonotes.