Shapefiles are the file type that is uploaded to your organization's Geography and will define your organization's service area. If you are looking for information on how to add a Shapefile to your organization, take a look at the Upload a Shapefile article.
SeeClickFix requires the full ESRI shapefile bundle for upload. That will include a .shp, .prj, .shx and .dbf file (at a minimum), projected in WGS84 (SRID 4326) and all packaged as a ZIP archive. Additionally, the layers must be either a Polygon or Multi-Polygon (most typical) or a PolyLine (for streets).
We cannot accept files with Z or M features.
Here is a list of possible shape types, and our support for them. We support PolyLine and Polygon:
ESRI has a full-length technical description of Shapefiles and how to create them.