If I understand your question, you are asking how to join quilted pieces together to form a larger quilt. This is not as difficult as it would first appear. It is a matter of first sewing the fronts together using a quarter inch seam allowance as if it were not quilted. Fold your backing and batting out of the way and attach the pieced top. When quilting smaller sections, you do need to be careful not to quilt in the seam allowance you plan on attaching to another piece.
I then put the quilt face down on a table so that it is smooth. Overlap the batting only, making sure the top stays flat. I then carefully take a pair of scissors and cut thru the overlapped batting using a curved or wavy cut. This will allow the batting to butt against each other tightly. Remove the excess batting.
The next step would be to attach the free ends of your backing. The method I use is to fold one side over the other and using an applique stitch hand stitch these together neatly. I just pull a chair up to the table that the quilt has been smoothed out on. Stick straight pins in to be removed as you approach that area.
Many quilters use this method of quilting smaller sections of their quilt on home sewing machines and then piecing the sections together. You may wish to check Quiltinaday.com. Eleanor Burns did cover this on her PBS show. Hope this is helpful.