Sensors are those electronic components which can sense the environment around us and convert that environmental parameter into an electrical signal.
Actuators are those components which give you mechanical output from an electrical signal.
There are some sensors that work similar to the human senses. As different parts of our body sense environmental parameters and convert them into neural signals, the electronic sensor also senses the environment and converts it into an electrical signal
We can see things around us due to reflection of light
Ultrasonic sensor can measure the distance of any object from itself
We can hear the sound around us with our ears
Microphone sensor can measure the level of sound in atmosphere
Our nose helps in detecting various smells
This sensor can sense different gases present in atmosphere
We can feel the touch of different things on our skin
This sensor can sense the human touch
Digital Sensors
Digital Sensors are the one which gives you output as 0 or 1. Some of the examples of digital sensors are IR sensors, PIR sensors etc.
Analog Sensors
Analog Sensors are the one which gives you output anywhere between 0 to 1023. Some of the examples are Light Dependent Resistor (LDR), Gas sensor etc.
You can also compare actuators with human body muscles. As our muscles exert mechanical actions to the environment which then get converted into movement of our hands or legs, actuators do the same thing.
Muscles provide the mechanical force to move the joints in our body and that results in the movement of hands, legs or other body parts
Motors can provide mechanical force to cause the movement of component attached with it
Sensors and Actuators both are the components which can be used with a micro-controller like Arduino.