What are parables? And why did Jesus use them

what are parables? and why did Jesus use them
In a nutshell, parables are fictictious stories or tales that demonstrate or teach either a religious styled principle or moral attitude. They were used as a teaching tool to reinforce his doctrine. The story was the example of the right way ( and sometimes the wrong way) of doing something.

A parable is a brief, succinct story, in prose or verse, that illustrates a moral or religious lesson. - From wikipedia "parable"

Jesus used parables for different reasons. There were a lot of people trying to catch Jesus saying something against the government or contradictory to the beliefs of that culture. Parables came in very handy because he could disguise his teachings, and therefore avoid prosecution from the government. The NT describes situations where the Pharisees and the Sadducees tried to trip up Jesus in his words. He used parables to get his point across.
Jesus also used parables to teach the doctrines of His gospel in a simple manner. For example, he used the culture marriage in the parable of the ten virgins to describe how his second coming will be swift, and only those that are prepared will be able to join him. He compared preparation for his coming to oil in a lamp that burns during a marriage ceremony at night. Notice that those virgins that did not have oil (five of them I think) could not just borrow oil or quickly go get some. It was too late. Jesus was explaining that when He comes in all his glory, it will be too late to repent at that time, or hurry and pray or read our scriptures. It is a parable about being prepared and not procrastinating. Let me know if this helps.

It was a common method of teaching esp doing the time of Christ.
It was using stories that the people could understand. In today's socieity, it may have been stories of walmart or stores of driving a car or if talking to people in the projects stories about housing officials