I don't mean to insult, but you said you're a novice at sewing machines.
The reason the threads are bunching up underneath is because the bobbin thread needs to be pulled up before starting...just like in quilting.
PULL UP THE BOBBIN THREAD by taking one stitch manually. Here's a 1 minute video to show how to
http://www.youtube.com/watch?v=UEmMYMjWUo8 (hold top thread, take one stitch manually, pull up bobbin)
When turning the corner IS YOUR NEEDLE IN THE DOWN POSITION? ... it should be in the down position, turn fabric, then sew.
Hope this helps
Stitches look GREAT from the side we can see....what's the other side look like?