Video explanation
A cutaway uses red upper thread and blue bobbin thread to show needle descent, loop formation, hook capture, passage around the bobbin case, interlocking and take-up. The recording demonstrates speed, step, handwheel and magnification controls; the author credits a skill.
A loop forms as the needle rises
The needle carries the upper thread through the fabric, then a loop appears as it rises. The hook approaches the needle to catch it; their timing matters.
Two threads interlock in the fabric
The red upper-thread loop passes around the bobbin case and interlocks with the blue lower thread. The inset shows the interlock; this depicts a lockstitch, rather than every stitch type.
Take-up and tension complete the stitch
The final phase raises the take-up lever to tighten the loop. Balanced upper and bobbin thread tension keeps the interlock within the fabric.
Drive and feed must stay synchronized
Labels identify a crank-slider, timing belt and feed dog, with a ×2 hook-shaft schematic. These illustrate coordinated motion; the animation does not establish calibration values for a real machine.