1. A reflex is an automatic response to a stimulus. For example: If I touch a hot plate, my hand will automatically pull away from the heat. Another example is the pupillary light reflex. If you turn on a light in a room, your pupils will shrink in order to limit the amount of light entering them. This helps the eye adapt to rapidly changing light. So from this, you can see that reflexes generally function to protect the body, and allow it to react quickly without conscious thought.
So in our example with touching something hot, a heat receptor produces a nerve impulse that will travel along a sensory neurone to the spine, which will then be connected by an interneuron by a synapse which is connected to a motor neurone by another synapse, and the impulse will travel from the motor neurone into the effector (in this case, muscle) and cause it to contract and move away from the heat.