Where have you been? I've been missing you. Was hoping your health is good.
Those with more experience will explain it better than I can but I will say:
You put the walking foot on the machine when you have your quilt sandwich ready to quilt. Check your user manual to see what stitches you can use when you have the walking foot on. YOU CAN NOT REVERSE on most machines. You have that brand new fancy machine so I don't know about that but I would say no reverse.
The walking foot keeps the top fabric moving at the same speed that the feed dogs are pulling the backing.
Without the walking foot the top will pull harder than the feed dogs and you get wrinkles and puckers.
How'd I do? I stole the information from another post I read today. I am going out now to look for the link and will edit.
This is a good one but not the one I had in mind.
http://www.quiltingboard.com/t-40867-1.htm
I found it! Read LoriS response in this post. It explains it perfectly.
http://www.quiltingboard.com/t-48833-1.htm#1145506
Good luck.