Fuses are a product used to put in any type of electrical circuit to protect the important components in that system. This is done by limiting the amount of current that can pass through a fuse. When too much current passes through a fuse, the fuse simply breaks. Below is a picture of one of many types of fuses. The two metal ends are the positive terminal and negative terminal. The metal filament inside in the fuse is what brakes when the current rating is greater then what the fuse can hold. When the metal filament inside breaks the other components inside the circuit are saved but not the fuse because fuses are meant to break only to protect the other components such as the other resistors.
http://media.digikey.com/photos/Bel%20Photos/5ST%20SERIES.jpg
Circuit Breakers
Circuit Breakers are quite similar to fuses, but instead of being a one time use, it can be used over and over. This is a Circuit Breaker designed to save the homeowner some money. For example everyday we do something that requires electricity, like plugging in devices in outlets to charge a phone, turning on the TV or even using the microwave. All of these devices put more current into the house hold and if too much current is present the electrons in the wire start to move faster, which can be problematic. Too much current can have a surge of current which leads to other devices in the house, causing them to break or even burn down the house. The circuit breaker comes in before any of that happens.
Below is a typical circuit breaker switch inside a circuit box someone has in their house. This particle ciruit breaker is on which means that it is constantly detecting the current flow as it travels from right to left in this photo. The current flows through the Bi-Metallic strip and into the purple contact. When the current flow is greater then what the circuit breaker can hold, the Bi-Metallic strip will heat up and expand to the right, closing the switch. The closed circuit breaker results in parts of your house having no electricity, until you press the switch on again.
https://www.youtube.com/watch?v=GSh0f94JwaA
This is how it looks like when the circuit breaker is off. Meaning that no current is going into or out the system until the switch is turned back on. As you can see the purple contacts are no longer touching.
https://www.youtube.com/watch?v=GSh0f94JwaA