The Singer 221 manual has a diagram of the pathway of the thread on a Featherweight:
The thread, of course, starts at the spool pin then goes down through the first thread guide (1).
Numbers 2, 3, and 4 involve bringing the thread through the tension knob.
- After leaving thread guide 1 bring the thread down into the tension discs from right to left (2).
- Either hold the spool or hold the thread firmly against the machine between 1 and 2 so that you can pull the thread up under the take-up spring (4) and yes, 4 then 3.
- Pull the thread gently until it goes into the retaining fork (3).
Now simply take the thread through thread guide 5 (the hook above the tension knob) and then through the take-up lever (6).
After that there are three more thread guides (7,8,9) and then the needle (10).
Made sure the needle is in the machine correctly. It should have the flat side towards the left when inserted. The thread goes through it from the right and comes out on the left.
The upper threading is done.
If you haven't threaded the bobbin see this post on how to do it.
Hold the threaded bobbin with the thread coming off the top towards you.
It's easiest if you hold the bobbin in your right hand and the bobbin case in your left hand. I'm holding it in my left hand in the photo because I'm holding the camera in my right hand.
Place the bobbin in the bobbin case and pull the hanging thread up into the slot in the case.
Keep pulling that thread so it slides up through the slot and under the tension and comes out the tiny notch further up in the case.
Now it's ready to be put in the sewing machine.
Hold the bobbin case by the latch with the thread coming over the top and place on the stud in the machine. Let go of the latch and push the bobbin case back so the latch catches in the groove in the machine. It should look like this:
Make sure there's at least a couple of inches of thread hanging out.
Put the bed extension down.
One last step and you're ready to sew. The bobbin thread needs to be brought up. Hold the top thread while turning the balance wheel towards you. The needle will need to go all the way down then back up to its highest point.
The bobbin thread should now be drawn up (you can pull the needle thread some to help it up). The bobbin thread is the loop of white thead coming up in the photo above. You can take something (pin, small scissors) and while holding the needle thread bring them under the foot and help get this bobbin thread all the way out. If you use something metal don't scratch your sewing machine throat plate or drag it across the feed dogs -- you'll be pulling that bobbin thread up everytime you change the bobbin and don't won't to always be scraping against the metal or in time it will show.
Both threads are where they should be and you're ready to sew!
Remember to hold the threads as you start sewing or one will get sucked under and it'll jam. If you need other information about sewing with a vintage Singer sewing machine I have some posts up under the tab Vintage Sewing Machine Basics.
Also, Featherweights didn't have seam guide markings on their throat plates originally. I've put a sticker I bought for this onto mine that you can see in the photos. It stays in place but can be peeled off easily if I want to remove it.