From Bushwalk Australia
KML stands for Keyhole Markup Language and in named after Keyhole Inc., the company that first develop it. It is based on XML which is a metalanguage that allows users to define their own markup languages. Markup languages are a modern system for annotating a text file so that it can be read and interpreted by computer software. The markups or annotations are instructions used by the software program.
Although originally developed for Google Earth, KML is now an international Standard of the Open Geospatial Consortium (OGC). It is an open standard officially named the OpenGIS® KML Encoding Standard (OGC KML).
The simplest KML files are created in Google Earth as a "Place". They can include placemarks, descriptions, ground overlays, tracks, polygons, web links, pictures and other features that can be easily added in Google Earth. You create the "place", and then right-click and save the KML file. Multiple places can be included in a single KML file. KML files can also be displayed in other 3D Earth browsers (geobrowsers) implementing the KML encoding.
At a minimum, each place must always have a longitude and a latitude. Giving a placemark a "name" is also helpful.
The following example KML file was created in Notepad and saved as Example.kml. This would appear in Google Earth as a yellow pin-cushion marker with the name "Mount Ossa".
<kml> <Placemark> <name>Mount Ossa</name> <Point> <coordinates>146.03296,-41.87072</coordinates> </Point> </Placemark> </kml>
KML files are very often distributed in KMZ format, which are a compressed file format using the ZIPv2.0 standard and have a .kmz extension.
You can also create KML files from a spreadsheet (see forum topic). You will need a minimum of three columns for longitude, latitude and name, then list your place by filling out as many rows as you wish. The name and order of the columns is important. You could for example use this information from the list of high places, or any other similar list. Save the file in CSV format and use one of the free online CSV to KML converters. For a more detailed approach, download and install a KML editor.