Objective: Learn and correctly use the essential sewing vocabulary and machine concepts you will rely on in every project, so instructions and later lessons make immediate sense.
Before you sew sellable items, you need a shared language. On the MC6650, the needle moves up and down through the needle plate while the feed dogs — the small metal teeth under the presser foot — grip the fabric and pull it toward the back at a set rate; this is what moves your fabric, not your hands. The presser foot holds fabric flat against the feed dogs so stitches form evenly. Stitch length controls how far the feed dogs advance between stitches (longer = bigger stitches, good for basting; shorter = tighter, stronger seams). Stitch width matters for zigzag and decorative stitches, setting how far the needle swings side to side. A straight stitch has zero width. The seam allowance is the distance between the fabric's raw edge and your line of stitching; a standard is 5/8 inch (1.5 cm), and keeping it consistent is what makes a garment fit and look professional. A backstitch (also called a lock stitch or reverse) means sewing a few stitches backward at the start and end of a seam so the thread doesn't unravel. Thread tension controls how tightly the top and bobbin threads interlock; balanced tension hides the knot inside the fabric layers. The MC6650 is computerized, so stitch length, width, and selected stitch appear on its LCD screen rather than on mechanical dials, which means you set them by pressing buttons and reading the display.
Example: Imagine making a simple fabric pouch to sell. You select straight stitch number 1 on the screen. The display shows length 2.4 and width 0.0 — a normal straight stitch with no side-to-side swing. You line your fabric's raw edge up with the 5/8-inch guide mark on the needle plate (your seam allowance). You press the reverse button to backstitch three stitches, release it to sew the seam forward, then backstitch again at the end to lock it. The feed dogs carry the fabric; you only guide it. The result is an even, secure seam that won't pull apart when a customer uses the pouch.
Try it: At your machine, identify and say aloud (or write down) these five parts/settings: feed dogs, presser foot, needle plate seam-allowance guide, the reverse/backstitch button, and the stitch length value on the LCD. Then select a straight stitch and change the stitch length from its default to 4.0 and back to 2.4, watching the screen update. Note in one sentence what a longer stitch length would do to a seam.