There are three required files for a shapefile. In Windows Explorer, look for the following extensions after your shapefile name:
- .dbf (dbase file, i.e. the attributes)
- .shx (index file that connects the .dbf to the .shp)
- .shp (geometry)
Then there are several that are nice to have, but are not always available. One example: .prj file (projection file)
ESRI Shapefile - components list
To ensure that you are sending all the components of a shapefile, I would do as jborgion suggested and Zip them, then send the Zip file to the other user.
Chris Donohue, GISP