Many habitual sewers like to sew by hand if possible for smaller projects, since all it requires is some finger dexterity, a needle, and some form of thread. Sewing machines can create stitches and embellishments of great beauty, but as with all electronic devices sometimes their constituent parts have complications. The bobbin, which holds the thread beneath the machine, is one of those pesky things sewers have to deal with.
If you recently purchased a Brother sewing machine (specifically the LS 2125), you may think that you need to take out the bobbin and the holder in order to thread the machine. But you don't need to remove everything, just the bobbin holder. The directions for this machine are very poor in showing a good graphic on how it all assembles back into place. Hopefully this helps you.