After a quilt top is pieced, it's time to make a quilt sandwich: backing, batting, and quilt top.
These layers need to be basted together to hold them temporarily. A quilt needs to be well basted to prevent shifting of the layers while quilting, which could cause tucks and wrinkles.
It seems that the most common form of basting is pin basting. You can also baste by hand sewing large basting stitches, or by using basting spray.
Amanda Jean at Crazy Mom Quilts shares simple instructions for pin basting:
The ribbon retreat also shows how to pin baste a quilt, including using a spoon to help close all those safety pins:
And my favorite directions for finishing a quilt, including pin basting, are shared by Allison from Cluck Cluck Sew: