a walking foot is for straight line quilting- like stitch in the ditch- or cross hatch- used with the feed dogs up- working
a darning foot (sometimes called a hopping foot) is used for free motion quilting- stippling/meandering- designs- with the feed dogs down (not used so you can easily move the fabric around)
and it takes practice- start on small items (like pot holders/place mats) as you become comfortable with that size try a bit larger- and work your way up to quilts