Once your quilt top is assembled, it's time to baste, which is another term for putting all the layers of your quilt together (backing, batting and the quilt top).
My quilt top is about 68" x 88", so I bought 5.25 yards for the backing. It was just enough. I don't go by the rule that your backing and batting need to be 4" larger on all sides of your quilt top. I like to squeak by with as little waste as possible.
I pin baste my quilts with curved safety pins. There is a tutorial here.
And now you are ready to quilt! I plan to put together a tutorial for next week on free motion quilting.