Bobbem is not right,tread knotting,cant sew

IT CAN BE THE TENTION SCREW ON THE BOBBIN CASE SOME TIMES THE BOBBIN SCREW CAN LOOSEN SO WHAT HAPPENS THE THREAD GET TANGLE UP IN THE BOBBIN CASE AND THAT BECOMES A PROBLEM 1-YOU CAN TRY AND TURN THE SCREW IN THE BOBBIN CASE TO YOUR RIGHT JUST A LITTLE FROCTION EACH TIME YOU DO THAT TRY SEWING SEE IF THERES ANY CHANGES 2-MAKE SURE YOU TREAD THE SEWING MACHINE RIGHT AND CHECK THE POSITION OF YOUR NEEDLE SEE IF IS SET CORECT CAUSE IF THE NEEDLE IS NOT SET RIGHT THAT CAN ALSO BE THE PROBLEM OR MAYBE WRONG NEEDLE. REMINDER START 1- CHECK NEEDLE 2-CHECK SEE THAT THE SEWING MACHINE IS TREADED RIGHT 3-THEN TRY THE SCREW ON THE BOBBIN CASE 4-CHECK SEE IF THE SEWING MACHINE NEEDS OIL.

It's called bird nesting or thread nesting.

Install a brand new needle.
Remove the top thread from the machine.
ALWAYS RAISE the presser foot and rethread from the beginning.
Set the upper tension to the midway point and then tweak it.

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When you thread the top do it with the foot in the up position. As you thread you should notice the ease of movement through the tension, holes, etc. If you come to a point it is sticking, check why. The tension could be a problem. Anyway, if you don't seem to have a problem hear then put your foot down. Pull on the thread to see if it is stuck or not moving with an extreme amount of difficulty. You may need to lower the tension. A good starting point is 3. I expect your tension is the problem. If it is still the problem then lower the bobbin tension slightly. By the time you finish the knot should be in the middle of the fabric. Sometimes there is one more problem It is the thread is poor quality and is unravelling in the needle hole. Observe this closely as you sew. You know what to do if this is the problem.

Try changing the needle if that doesn't work try adjusting the foot pressure. I had that problem with one of my quilts and It was the presser foot. I used google to find a lot of answers for machine problems, You would be suprised how many answers and utube videos you will find to show you how to fix things.

The carrier and bobbin are removed. Place the thread in the carrier with the thread dispensing counterclockwise. Place the thread between the metal pieces (tension). let the carrier hang from your finger and bob it slightly. It should extend one inch. If it doesn't then you can adjust it by turning the small screw slightly until it does what I said. Now, replace this assembly. The top tension you can start at three. The sewing should be an even pull between the upper and lower thread. If the thread knot is in the center of the material it is right. If the knot is under the material then raise the upper tension. If the knot is on the upper material then you should lower the upper tension. The key is to start with the bobbin tension correct and adjust the upper tension until the knot is in the center of the fabric

Put the top tension on 3. The bottom bobbin carrier remove. The little plate on the carrier has a screw to tighten and loosen for the bottom tension. Allow the thread to drop the carrier about two inches from your hand and move up and down lightly. The carrier should extend slightly when you do this. If it doesn't do it then loosen. If it does it too far then tighten. Make sure that your bobbin is rotating counterclockwise. The top may have to be adjusted by the fabric you are sewing but three is a good start.

First check in the bobbin area for lint, bits of thread wrapped round parts.

Then make sure your needle is oriented and inserted fully.

Also when starting a seam be sure to grasp both of the threads and hold them as you start to sew.

If you still have problems, make sure your thread and needle are suitable for your fabric.

Since you don't really say where it knots and breaks ... it could also be a damaged needle plate.

check the bobbin case tension--turn the screw to the left to tighten ---turn the screw to the right to loosen
also check the needle to see if it's damaged
also make sure the bobbin is threaded correctly & placed correctly in bobbin case
check for lint or loose threads in bobbin area
check for warped bobbin

check the treading of the bobbin. it isn;t like my old singer I followed the directions in the manual.

Are you sure you have the bobbin the right way round in the holder....when you look at the bobbin and tug the thread, the bobbin should move clockwise.
Pull out the foot pedal and use bsr2 with the start/stop button.
Bring bobbin thread to top of work before starting to sew. This may help knotting problem