It's very hard to tell you all about the impressionism and realism characteristic in just a couple of sentence. But with every piece of art movement, you can always start with the time, culture and society. They are the main factors that contributes greatly to the foundation of any art movement.
For example, Monet and the rest of the impressionism's main concern and purpose in composing an artwork is to capture their new Parisian lifestyle. To capture the feeling, the atmosphere. It's very sponstaneous! Monet worked all his life to capture fleeing moments with the change of light. I have often compared the impressionism movement to photography.
(sorry really dont have time to explain more)
