It’s really helpful to be familiar with Esri and shapefiles, as this fairly advanced work intended for organizations that work with mapping data. The minimum required files needed within the shapefile are the .shp, .shx, .dbf, and .prj files. These files make up the geometry/shape that you’re uploading, the information that allows you to pan and zoom, and other attributes needed to display the shape. You can upload compressed (Zip) files or individual files. The shapefile can only contain polygons, cannot contain more than 10 shapes totaling 10,000 points, and needs to be 10MB or smaller. If you upload a zip file, it can only contain one shapefile.
To upload a file, go to Contacts in the top main navigation bar, then click Manage Mapping Selections on the right, then click the Create button at the bottom, and then click Upload Shapefile at the top. Here you will have the option to upload a zip file, or to upload files individually.