It started as a functional piece of clothing during the 1900s worn by people riding horses to protect their under layer of clothing from dust — hence the name, duster. They were also worn by cars because of the motorcars were open and were driven on dirt roads during that time.
Today, they have become a new "it" fashion statement. Dusters are made of lightweight fabric and usually are similar in form to a trench coat. Think of them like a spring/summer trench coat. For a casual look, wear a pair of denim cut-off shorts and a loose t-shirt underneath the duster. If you want to dress it up a bit, go for a skirt or a pair of nice shorts with a cute top and heels underneath the duster coat. Just make sure the layer of clothing underneath your duster is relatively tight so that your outfit doesn't swallow you.
Celebs, like Kendall and Kylie Jenner are rocking the trend (Kendall and Kylie even added a duster coat to their Topshop collection). Put a modern twist on this turn of the century trend and rock a coat duster.