Symbology refers to the way each layer on your map looks - the different icons, their colors, and their size.
There's a lot of theory and many rules for symbology. Check out the links and videos below to learn about ways to change the way things look on your map.
Remember, you may not need to change anything in this map because we will export the shapefiles back out to ArcGIS Online, where you can change the symbology, too.