A bobbin is an integral part of a sewing machine. The bobbin thread is wound onto the bobbin, and once the assembly is in place you can create an interlock stitch, looping two threads together.
Open the hook cover by raising the needle. This can be done by turning the fly wheel towards you.
Remove the bobbin assembly by pulling on the latch. The latch is in the middle of the bobbin assembly and resembles a zipper pull.
Place the wound bobbin in the bobbin case. Make sure the thread unwinds in the same direction as the arrow on the case.
Pull the bobbin thread into the bobbin case slot and then draw the thread under the tension spring and into the delivery eye.
Place the bobbin case back into the bobbin assembly and ensure that the horn is placed back into the recess of the hook race.
If the bobbin thread is snagging when you sew, you might have the bobbin thread wound in the direction opposite of the arrow on the bobbin assembly.