I managed to get Google Earth layer, but when I add my GPS gpx files, all are hidden under the Google map...
How to put them onto Google Earth layer?
I am guessing the GPS gpx file gets added as a point layer.
You should be able to see the GPS points on Google layer.
You need to first convert your gpx file to a kml or kmz.
I prefer GPSBabel to do this, but over there years several other software packages that will do the same thing have been published.
This Article on Importing GPS Tracks into Google Earth gives you a couple more plus an overview on the whole process.