You layer all three together at the same time. You can either pin-baste the three layers, or baste it with thread. You put the backing down first, wrong side facing you, then spread the batting over top of that, then the quilt top, making sure that your backing and batting are about 3-4" larger than the quilt top on all four sides. Tape, pin, or clip the backing and batting to the surface you're basting it on, making sure that they're both very smooth, no puckers anywhere, then smooth the quilt top and secure it with tape, pins, or clips. Then begin to baste with either small (1") safety pins or thread (making your stitches about 1-2" long, and your rows about 3-4" apart. If you're going to hand quilt the quilt you will need to do this in both directions, up the length and across the width of the quilt. If you're going to machine quilt it, then you can get away with only basting in one direction, usually bottom to top is best.