Free motion quilting is the one thing you do on a sewing machine where the machine stops helping. The feed dogs stop pulling, and from that point every stitch is exactly as long as your hands decided it would be. That is why it looks intimidating, and why it gives you loops and swirls a straight stitch cannot reach.
This one follows Leah Day, who teaches it on an ordinary domestic machine rather than a longarm and is blunt about the first hour looking terrible. She starts with stippling: one wandering line that curves back on itself and never crosses over. None of it works unless the three layers are held flat, so if your sandwich is not pinned or sprayed yet, baste the quilt first. Quilting a loose sandwich pleats the backing, and you will not see it until you turn the quilt over.
Feed dogs down, or stitch length at zero
The feed dogs are the little teeth under the needle plate that walk fabric away from you at a fixed rate. Free motion means taking them out of the job. Most machines have a lever that drops them below the plate; some older ones came with a cover plate instead.
There is a third route that gets skipped in most tutorials: turn the stitch length dial down to zero. The teeth still sit up but they stop travelling, so they hold the fabric without carrying it anywhere. Leah quilts this way on purpose and reckons the stitch looks better for it. Either route is right, as long as the machine has stopped deciding where the fabric goes.
Why your stitches come out uneven
Stitch length is now a ratio between two speeds: how fast the needle goes up and down, and how fast your hands slide the quilt under it. Quick hands over a slow needle stretch the stitches long. Barely moving hands at the same speed make them microscopic. The wobble in your first practice block is that ratio drifting, not a fault in the machine.
The fix is dull and it works. Pick one machine speed and stay on it, let your hands do all the varying until the line looks right, then hold that hand speed. Do not take a ruler to your stitches. Look at the line and decide if you like it.
Gloves and a slider sheet
Two cheap things carry most of the difficulty. Quilting gloves with grippy fingertips stop your palms skating over the cotton, which is the real reason a quilt feels out of control. A slider sheet is a thin slippery mat that lies across the machine bed with a hole cut for the needle, and it drops the drag under a heavy quilt to almost nothing.
Free motion or walking foot?
These are the two ways to quilt a finished top and they do different work. A walking foot feeds all three layers at the same rate and gives you straight lines, grids and long gentle curves with the feed dogs still running. That is straight line machine quilting, the easier of the two to pick up. Free motion gives you stippling, loops and feathers no walking foot can be steered into. Most quilters use both on one quilt.
Where this sits in the order of things: piece the top with a true quarter inch seam, add the borders, baste the layers, quilt them, then bind the edges.
What goes wrong, and what to do about it
A knot on the back where you stopped. Your hands paused while the needle kept going. Any time the quilt is not moving, lift your foot off the pedal.
Jerky stitches, or plain ugly ones. Usually hand speed. Slow your hands and let the curves come out bigger before you try to make them small. Everyone's first blocks are ugly, and hands take mileage.
Stranded in a corner. Filling at random leaves a bare patch ringed by finished quilting with no way in. Work in rows, the way you fill a page of writing.
The bobbin thread snarls at the start. Pull the bobbin loop up through the quilt before the first stitch, every time. A bobbin wound evenly helps, and small washers that sit under the bobbin stop it spinning backwards.
