The are many types of switches but in this section we'll just go into mechanical switches. Switches allow or stop the flow of current or control which path it is to take.
The simplest switch is the knife switch, which is usually a simple lever that conducts electricity that moved against a contact. So moved against the contact it allow current to flow from the lever to the contact and moved away from the contact it will not allow current to flow.
Switches also come in a variety of forms single and double pole and single and double throw. Single pole means that the switch has one contact. Double pole means there is two contact and the switch can move between them. Single throw means that there is one lever attached, double throw means there is two levers attached, like two switches 'tied' together.
Other switch types
Toggle - These are very similar to the knife switches except they are normally enclosed and spring loaded so they only rest in certain positions.
Push Button - Push button switches are spring loaded switches that come in two types, normally open (NO) (does not allow current to flow) and normally closed (NC) (allows current to flow) and pushing them changes their state and they return to their original start when you release them.
Reed - Reed switches are to very small contact (normally open) placed very close together in a glass tube. If you place a magnet close to them they bend and complete the circuit and recover to their original position once the magnet is removed.
Rotary - This is a dial, like the channel changer on an old TV. When you turn the dial round different connections are made.
Slide - These are similar in function to the other but these switches work by a contact sliding over other contact to complete the circuit rather than levers.
Mercury - This switch has two contact close together but not touching enclosed in a glass tube with a blob of mercury (a metal that is in liquid form at room temperature). When you tip the tube it completes the circuit or visa versa.