Idioms are something we use every day - from literature to casual conversation. An idiom is something like a metaphor that doesn't use its actual meaning and is usually used as a comparison. Unless it's a very formal text, it's always a good idea to use idioms. They can help to prove points or make for some good comedic timing. It's easy to learn these phrases because of the countless online dictionaries like the Merriam-Webster dictionary. Also, this website has a list of popular idioms you can use to enrich your language arsenal.