Objective: Practice controlled straight-line sewing, backstitching, and corner pivots so your seams are even and secure before sewing real project pieces.
Clean sewing comes from consistent seam allowance, steady speed, and locked seams. The seam allowance is the distance between the needle and the raw edge of the fabric; 5/8" (16mm) is the standard for home sewing, and the MC6650's needle plate has an etched guide line at 5/8" to steer against. Keep your eyes on that guide line and the fabric edge, not on the needle. Set a moderate speed with the slider and let the feed dogs pull the fabric; you guide, you don't push or pull, which would bend the needle or stretch the seam. Backstitching locks threads so the seam won't unravel: sew forward a few stitches, press the reverse button to go back over them, then release and continue forward; repeat the reverse at the very end. For a square corner, stop with the needle fully down in the fabric (press the needle up/down button so the needle stays embedded), lift the presser foot, rotate the fabric 90 degrees around the needle, lower the foot, and keep sewing. The needle acts as a pivot pin so the stitching stays continuous with no gap.
Try it: On a 6x6" square of scrap woven cotton, draw two parallel lines 5/8" from two adjacent edges with a fabric pen. Sew along the first line: backstitch 3-4 stitches, sew forward keeping the fabric edge on the 5/8" needle-plate guide, and when you reach the drawn corner stop with the needle down, lift the foot, pivot 90 degrees, lower the foot, continue to the end, and backstitch to finish. Inspect: the stitch line should stay an even 5/8" from the edge and the corner should be a crisp L with no loose stitches.