We tested two apps that allow exporting recorded tracks to a .KML file and you can install them from  Google Play / App Store by scanning QR codes below.

https://play.google.com/store/apps/details?id=eu.basicairdata.graziano.gpslogger
https://itunes.apple.com/us/app/mytracks-the-gps-logger/id358697908?mt=8

These apps are only our suggestion and you can use any app you want if it allows exporting recorded GPS tracks to a .KML or .KMZ file.

To upload .KML or .KMZ file click on the “KML” tab and “Upload your KML file” button. Then upload your KML file (or paste the URL if it’s already hosted somewhere).

Sometimes .KML files may not work properly and tracks won’t be displayed on a map.
In that case open your .kml file in notepad and “Save as type” with .kmz extension.

If you are not going to add any custom points then you’ll have to set center map point for your KML tracks. You can do it by clicking “Custom Center Point” field and adjusting marker position (this marker won’t be visible in published post).

Recorded tracks from the file won’t be visible on map until you will save the post (you don’t have to publish it yet, you can save it as Draft).