This is a high-level answer as you've not given any specifics.

Reading KML is basically the same as XML (KML being a subset thereof).

Some possible resources:

http://stackoverflow.com/questions/8342337/parse-kml-file-with-php

http://www.boards.ie/vbulletin/showthread.php?p=71913675

http://web.stefanproell.at/wp/2010/01/parsing-kml-files-with-php/

Then you just take the variable that you've read your data to and output it to the database.

This is a high-level answer as you've not given any specifics.

Reading KML is basically the same as XML (KML being a subset thereof).

Some possible resources:

https://stackoverflow.com/questions/8342337/parse-kml-file-with-php

http://www.boards.ie/vbulletin/showthread.php?p=71913675

http://web.stefanproell.at/wp/2010/01/parsing-kml-files-with-php/

Then you just take the variable that you've read your data to and output it to the database.