As far as I understand, you have to use the play/generate button to use the loops. I've tested out several 4 bar loops that I found on the net and they work fine.
I created a folder"guitars" in the loop folder and put the wav or mp3 files I found in there.
I chose the melody track for testing, put my chords in, chose a style, but muted the other instruments so I could hear the loops. I did the play /generate and it works.
Wyndham