This Instructable explains how to use a particular sewing machine, the Necchi belonging to the Noisebridge hacker space in San Francisco. It will be helpful in understanding sewing machines in general if you aren't familiar with them, but yours will differ in details.
A sewing machine stitch is different from a hand sewn stitch. The machine stitch consists of two threads, one on each side of the material to be sewn, which loop around each other to make one stitch. Thus a sewing machine has two threads, the main one visible on top of the machine, and a smaller bobbin of thread that's hidden away inside.
This instructable will show you how to remove and insert the bobbin, how to thread the machine, how to wind more thread onto a bobbin. Coming later, once I've taken more pictures: how to operate the machine.
Note: the foot pedal/power cord assembly is detachable, but can only plug in in one way. Also, there is an on/off switch on the right side of the machine. When it's on, a light will go on by the needle.
Step 1: Bobbin Insertion and Removal
The bobbin is held in the "free arm" part of the machine, directly under the needle plate. The bits that hold the bobbin are called, collectively, the trace. The bobbin is held in a case, which is held by the trace. There's a flap that pulls down on a hinge to reveal the bobbin trace. The bobbin case has a little lever attachment that pulls out to let it be removed from the trace (see first pic). The lever also holds the bobbin in the case so when it's held out, the bobbin can be removed (second pic).
To put a bobbin in the machine, hold the bobbin case with the open side towards you. Hold the bobbin you're going to insert so that the thread is wrapped around clockwise (see third pic). Slide the bobbin into the case, where it should fit easily without any pressure. The thread coming off the bobbin needs to slide through a small slit (fourth & fifth pics) and then under the tension flap to come out by the kind of bar that sticks out the other side of the case (sixth pic). Really the pictures are clearer than this explanation.
There is a tiny flat-head screw holding the tension flap down. This controls the lower thread tension but you'll probably never have to mess with it... if you do, be careful not to loosen it so much that the screw comes out and the flap falls off inside the machine.
Now that the bobbin is in the case, put the case back into the bobbin trace assembly (pic 7). The bar that sticks off the bobbin case fits into a slot on the trace assembly (pic 8). Close the door on the whole thing. Let the end of the thread hang out (pic 9). You'll take care of this hanging thread in the next step, threading the machine.
Step 2: Threading the Machine
The upper thread comes from a spool that is placed on top of the machine on one of the two pins provided for this purpose. The pins both can be pushed down into the machine and pulled back up out, as needed (pic 1).
The machine has been labeled with the order of operations for how the thread goes through. You can follow from 1 - 2 - 3 - 4 - 5 and you'll probably get it mostly right. For the detail-oriented:
1. first put the thread through the bits on the top as shown in pics 2 & 3.
2. next wrap the thread counter-clockwise around the tension dial. Looking down into the dial you'll see a pair of metal disks. Make sure the thread goes between the disks. See pics 4 & 5.
3. As the thread comes out the left side of the tension dial, catch it in the bent wire as shown in pic 6.
4. Bring the thread back up and through the metal looper, from right to left, as shown in pic 7. The looper has an opening near the back, you don't have to feed the thread through like for a needle. The looper moves up and down; if it's not up and accessible, turn the knob on the far right of the machine towards you gently until it moves up into position.
5. Bring the thread down through the open slot to position 5 and push it through the internal hook that's kind of visible in pic 8.
6. Slide the thread through the penultimate hook, just above the needle, as shown in pic 9. Thread the needle, from front to back, using whatever technique you can - often it is helpful to cut off a bit of the end of the thread, if it has become frayed. After it's through the needle, run it through the hole in the presser foot as well.
Finally, make one stitch by hand to bring the bobbin thread up through the needle plate. Hold a finger on the thread you just put through the needle to keep it from being sucked into the bobbin assembly. With the other hand, turn the knob on the far right side of the machine gently toward you, causing the needle to go down through the needle plate and back up again (pics 11 & 12). As it comes back up, it will bring the bobbin thread along, caught on the upper thread. You may need to pull the end you're holding a bit to get the loop up and visible (see pic 13). Pull the loop all the way through so the bobbin thread also runs out between the presser foot and the needle plate, next to the top thread, as in pic 14. Now you are ready to sew!
Step 3: Winding a Bobbin
Oh noes, the bobbin has run out of thread! What to do?
Pull the top thread out of all its little channels. As shown in pics 2 & 3, wrap it clockwise around the little disk atop the knobbly bits next to the 1 mark. This is the bobbin wrap tensioner. Put the thread end through one of the holes in the bobbin (from inside to outside). Push the bobbin down onto the winder shaft - on this particular machine, with this particular bobbin, you can't get it all the way down and there is no need to try. Push it down until it won't fall off, but don't force it any further (see pics 4 & 5). Push the bobbin on the shaft towards the right - there are 2 positions, right and left; right is for winding the bobbin.
Still holding the end of the thread, press gently on the foot pedal as in pic 6. The bobbin will spin and the needle will go up and down - this is OK (there's a way on most machines to release the needle assembly during bobbin winding, but on this one it's stuck). After a few wraps, you can stop and cut off the thread end you're holding, close to the bobbin (pic 7).
Now just press the foot pedal and let the bobbin wind up. Since the bobbin is sitting higher than normal, you'll need to use your finger to ensure the thread is wound evenly around the bobbin spindle, as shown in pics 8 & 9. Wind as much or as little as you need, cut the thread, and remove the bobbin from the winding shaft. Push the shaft to its left position, replace the bobbin and rethread the top thread, and continue sewing.
Step 4: Sewing a Straight Line
Place the fabric you want to sew into the machine. Lower the presser foot (this is very important). Press the foot pedal.
To backstitch, hold the lever on the far right side of the machine up (down?), and the feed dogs will push the fabric backwards.
Seam allowance markings on throat plate.
Step 5: Stitch Adjustments
Zigzag, stitch length, buttonholes (separate step?), tension
Step 6: Freehand Embroidery
Dropping the feed dogs. Embroidery hoop? Special foot.