Legacy:
Map documents (MXD) are ArcMap files. Version 10.8.x is the last release of ArcMap. If you are using ArcMap, use the option at the top of this page to see previous versions of the ArcGIS Server help for an example of publishing a map document.
If you are using ArcGIS Pro to create files to publish to ArcGIS Server, see Introduction to arcpy.sharing in the ArcGIS Pro help for instructions and examples.