Objective: Sew a complete envelope-back pillowcase cover to practice straight seams, seam allowance, and the MC6650's hands-free sewing features in one finished product.
Now that you can thread the machine and form a stitch, your first real project ties those skills together into something sellable. A simple envelope-back pillowcase cover (no zipper) is ideal: it uses only straight seams, teaches consistent seam allowance, and finishes fast. On the MC6650, confirm stitch #1 (straight stitch, center needle) is selected and set stitch length to about 2.4-2.5mm for strong, even seams. Use the engraved seam guide lines on the needle plate to hold a steady 1/2-inch (about 12mm) seam allowance by lining the fabric's raw edge to that line. Because the MC6650 has a built-in motor button, you can sew without the foot pedal: press the start/stop button to run and press again to stop, and slide the speed control to a slow setting while you learn so you can watch the edge. Always backstitch (reverse button) two or three stitches at the beginning and end of every seam to lock it so it won't unravel in use or washing. The automatic thread cutter button snips both threads at seam end, keeping your work tidy. The 'envelope back' means the back is made of two overlapping panels, so you can slip a pillow in without any closure hardware.
Try it: Cut one front panel 17x17 inches and two back panels 17x11 inches from cotton. Hem one 17-inch edge on each back panel: fold that edge under 1/2 inch, then 1/2 inch again, and straight-stitch it down. Lay the front panel right-side up. Place both back panels right-side down on top so their hemmed edges overlap in the middle and all outer raw edges align. Pin the four corners. Starting at one edge, backstitch, then sew around all four sides at a 1/2-inch seam allowance using the needle-plate guide, pivoting at each corner (needle down, lift foot, rotate 90 degrees, lower foot). Backstitch at the end and press the thread-cut button. Clip the corners, turn right-side out through the back opening, push out the corners, and press. Insert a pillow form to check fit.