To do straight line quilting, use your walking foot and feed dogs up. To FMQ, you need a FMQ foot or Darning foot and feed dogs down. The whole idea of FMQ is quilting without stencils or pantographs or drawing on your quilt. Do alot of practicing on paper first to get the hang of your design, do it without lifting your pen/pencil. Then make up some practice quilt sandwiches and do alot of practicing on that before going to your quilt. Just remember when you are FMQ.... relax and breath. If you feel like you are getting tense, stop for a while. They say drinking a glass of wine before FMQ helps. I dont like wine. But you get the idea. Most of all, have fun with it. Enjoy!
Tartan had a good point regarding having to turn your quilt with your wlaking foot on. If its a large quilt its a pain, but being new at FMQ may not be the best choice for trying tomake a straight line.