Here are a few of my favorite pressure "feet" to sew with!
This is a darning foot for your sewing machine. It is for stippling designs onto quilts or any other craft you may be doing! This foot allows you to do free-hand designs rather than just shooting through your quilt in a straight line with a regular pressure foot. (The one that comes already on your sewing machine).
A good way of practicing free-hand motions with your darning foot is to create a design on regular paper and then sew on the paper without any thread in your machine. You can also try this with your straight foot if you want to practice sewing straight, on a small curve, or zig zags.
This is a walking foot. It is used best when you have thick layers of fabric that you'd like to keep all together when sewing. I would do only straight lines with this - I've broken two needles on my walking foot trying to do a decorative stitch! On your sewing machine, there is a traction device to pull the fabric through as you are sewing..what this foot does is it has another traction device on top so all of your fabrics you are sewing together are pulled through at the same exact time. It is nice to have so that at the end of sewing two pieces of fabric together, you aren't stuck with one longer than the other!