I have never used a sewing machine before!!

the following may help. Most machines thread in a similar fashion.

How to Thread the VX 540 Brother Sewing Machine

Sewing Basics 1 How to thread your machine

There are some very basic things to do.

Install a brand new needle.

Remove the thread from the machine.

ALWAYS RAISE the presser foot and then rethread the upper thread. Confirm it is following the correct thread path. (Bird nests occur usually because the thread is not seated completely in the tension disk or the machine is threaded improperly.)

Verify the bobbin is installed in the bobbin case facing the proper direction and that the bobbin case is threaded properly.

Set the upper tension to the midway point (the factory standard), although this may need to be tweaked as machines change over time and use.

Pull the bobbin thread to the top and hold the thread tails. (This works for general sewing, not just quilting.)
How and Why to Bring up the Bobbin Thread

Slowly begin to test sew.

If it continues to create bird nests, then your machine may have a timing issue. Take it for service.

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basically the problem comes from incorrect thread tensions
the main thread responsible is the needle thread as the tension is far too loose
tighten up that tension and it makes the needle on the up stroke pull the thread around the bobbin carrier and collects the bobbin thread and pulls it up to the material
with the needle thread too loose the needle thread is wrapped around the bobbin carrier again giving you the 3 threads ( 2 needle threads and 1 bobbin thread and the tangle jams the bobbin movement

Here's a manual source. http://www.sew4less.com/product_details.php?ProductID=5990
This manual is available for PDF download: http://www.sewingmanuals.com/Sewing_Machine_Manuals/Singers.htm
Happy Sewing!

Hi I have bought a Toyota sl3304 overlocker. Unfortunately the manual is missing!!!! Can anyone help please.
Wendy

You can download a manual from http://www.singerco.com/accessories/manuals.html, just type your model number into the search field to locate it then download the pdf file to your PC. This is a basic Zig zag machine so carefully follow the manual instructions to wind a bobbin, thread up and stitch, just make sure you follow the directions to wind a bobbin, and then put it in the right way and click the thread into the tension spring.

This is going to be pretty veige, Im sorry but I have seen a lot of these go unanswered so hopefully this is at least helpful. All sewing machines have to do the same basic things, First the thread will go through a directional hole just getting it in the right spot, then it goes through the tension discs, then the take up spring, then the take up arm, then down through to the needle. I realize this this is veige, but I sure hope it helps.

you do need to provide more details.  start here - get a fresh spool of high quality all purpose thread such as Coats and Clarks or Metrosene thread, fill a fresh bobbin, install a new size 11 needle.  Follow the threading instructions even if you've threaded the machine a million times, read the instructions again.  try sewing on some basic cotton fabric.  You'll be able to determine if it's the machine.  Breaking thread can be the thread (it does get too old and fragile), the needle, the incorrect needle for the fabric, the wrong thread for the fabric, and a host of other things.  So try that and tell us more if that doesn't work. 

It really sounds like you have it threaded wrongly. You should find threading instructions in that manual.

Not sure if I am too late, but it's pretty basic. I have the same machine...

You have the thread on the spool with the thread on the left side (unrolling off the spool counterclockwise) and put it around the round thing on the front middle (looks like a snap sort of) and through the eye almost right in front of it (the loop) and hold the thread lightly then wrap the thread around the tensioner (the thing with the dial) to the left (counterclockwise) until the springs "pops" it into place. Then run the thread through the little hook thing (by entering from the left) then up to the eye (hole) that is in the little arms that raises and lowers (you might need to spin the wheel to get the arm in the right position) then you run the thread back through the hook thing (entering from the left) around the little half circle thing (by entering from the left) and finally in the hole in the needle...

hope it made sense, I tried to use laymen terms...

good luck!